Learn Hardcore Russian: Вчерашняя ссора оказалась пустой, и мы смеялись над ней за ужином. - Yesterday’s quarrel turned out to be pointless, and we laughed about it at dinner.

Вчерашняя ссора = the quarrel that happened yesterday (it identifies which quarrel).
вчера is an adverb = yesterday (it tells when something happened).

Your version Вчера ссора оказалась пустой is grammatically possible, but it means:

Yesterday the quarrel turned out to be pointless (the time of “turning out” is yesterday).

The original sentence with вчерашняя ссора talks about that specific quarrel from yesterday; it doesn’t specify when you realized it was pointless (maybe today, maybe later). So:

вчерашняя ссора — focuses on which quarrel.
вчера ... оказалась — focuses on when it turned out to be pointless.

Both are correct, but the nuance is different.

Why is it оказалась and not just была? What does оказаться add?

Both are possible, but they are not identical:

быть (past была) = to be (simple state, fact).
оказаться (past оказалась) = to turn out (to be), to prove (to be).

Вчерашняя ссора была пустой
→ The quarrel was pointless (a flat statement about its nature).

Вчерашняя ссора оказалась пустой
→ The quarrel turned out to be pointless — there was some result / discovery / realization. For example: at the time it felt serious, but later you realized it was pointless.

So оказалась emphasizes:

a resulting evaluation,
often some contrast between what you thought before and what you think now.

That’s why оказаться is very natural here.

Why does оказалась have the ending -лась? What are -ла and -сь doing?

The form оказалась breaks down like this:

оказать-ся → dictionary form оказаться (perfective, reflexive verb “to turn out, to prove to be”).
Past tense feminine singular ending: -ла.
Reflexive particle: -сь (reduced form of -ся after a vowel).

So:

оказал – he rendered (something)
оказалась – she/it (fem.) turned out (reflexive оказаться)

Here ссора is feminine, so the past tense verb agrees:

ссора оказалась
женщина оказалась
ситуация оказалась

The -сь is not optional; it’s part of this verb’s meaning. Without -ся, оказать means something different (“to render, to provide” a service, e.g. оказать помощь = “to render help”), not “to turn out.”

Why is it пустой and not пустая after оказалась?

This is a case issue.

The adjective пустой in the dictionary is masculine nominative (пустой стол – “an empty table”). But in the sentence пустой is:

feminine singular instrumental (it looks the same as masculine nominative, but grammatically it’s instrumental feminine).

Forms of пустой:

Fem. nominative: пустая (пустая ссора)
Fem. instrumental: пустой (ссора была пустой / оказалась пустой)

After verbs like:

быть (in many past/future uses),
стать,
оказаться,

Russian very often uses the instrumental for a predicate describing a resulting state:

Ссора была пустой.
Ссора оказалась пустой.
Он стал врачом.

So:

пустая here would be nominative;
пустой is instrumental, which is more natural with оказалась.

You can sometimes hear Ссора оказалась пустая, but оказалась пустой is the standard, idiomatic form.

What exactly does пустой mean about a quarrel? Literally it’s “empty,” right?

Literally, пустой = empty (no contents):

пустой стакан – an empty glass

By extension, with abstract nouns (like ссора, разговор, обещания), пустой often means:

pointless, meaningless, vain, about nothing important.

So пустая / пустая ссора or пустой разговор suggests:

it had no real substance,
it wasn’t worth it, nothing important was at stake.

Other close adjectives are бессмысленный, напрасный, but пустой is very idiomatic for a “silly, pointless” quarrel or argument.

Why is the pronoun ней and not её after над?

After most prepositions, Russian uses special “н-” forms for 3rd‑person pronouns:

она → её (gen/acc), ей (dat), ей/ею (instr), ней (prep)
But with prepositions you usually see: у неё, к ней, о ней, с ней, над ней, etc.

So:

Над ней is the regular combination: over / at her/it.
над её is wrong here.
над нею is also possible, but sounds more formal / poetic.

Case-wise, над governs the instrumental, and for она the form used with prepositions in this role is ней (or нею), not её.

Why does смеяться use the preposition над? Could I say смеяться о ней or just смеяться её?

With the meaning “to laugh at someone/something,” Russian uses:

смеяться над кем? чем? (instrumental)

Examples:

смеяться над шуткой – to laugh at a joke
смеяться над ним – to laugh at him
смеяться над ней – to laugh at her / at it

You cannot say:

смеяться её – wrong
смеяться о ней – sounds archaic / wrong in modern standard Russian with this meaning.

If you want “laugh about something funny that happened,” in practice you still normally use над:

мы смеялись над этой историей – we laughed about/at that story.

So: memorize смеяться над кем/чем for “laugh at / laugh about (in a teasing way).”

Why is смеялись (imperfective) used, and what would change if I said посмеялись?

Смеялись is past tense, imperfective, plural of смеяться:

мы смеялись – we were laughing / we laughed (without focusing on completion).

In this sentence, смеялись presents laughing as an ongoing/background activity during dinner.

If you change it to мы посмеялись над ней за ужином:

посмеяться is perfective = to have a laugh, to laugh for a while and finish.
It presents the laughter as a single, completed episode, something like “we had a good laugh about it at dinner.”

Both are correct:

смеялись – more neutral, process‑like, background action.
посмеялись – emphasizes that you did it as a complete action (had a laugh and that was that).

What does за ужином literally mean, and how is it different from на ужине or во время ужина?

За ужином literally is “at / over / during dinner,” using:

preposition за
- instrumental ( ужином ).

Common meanings with за + instrumental include:

being seated/located “at” an activity or table:
за столом, за обедом, за ужином, за работой
(at the table, at lunch, at dinner, at work)
doing something during that activity.

Other options:

во время ужина – “during dinner,” more explicit/neutral about time, slightly more formal.
на ужине – “at a dinner” as an event (a dinner party, formal dinner, business dinner).

Examples:

Мы смеялись над ней за ужином. – We laughed about it while we were sitting and eating dinner together.
Я познакомился с ним на ужине. – I met him at a dinner (event).

So за ужином fits perfectly for an informal family/normal dinner as the background situation.

Why is ужином in the instrumental case after за, and not, for example, ужина?

The preposition за changes meaning depending on case:

за + accusative → “for” (purpose, exchange, cause):
заплатить за ужин – to pay for dinner
спасибо за ужин – thanks for dinner
за + instrumental → place / context / activity, often “at / over / during”:
за столом, за игрой, за ужином – at the table, over a game, over dinner

In за ужином, за is used in the “at/during an activity” sense, so it must take instrumental:

ужином (instrumental singular of ужин)

Could I say Мы смеялись над вчерашней ссорой за ужином instead of using над ней? Is there any difference?

Yes, that sentence is completely correct:

Мы смеялись над вчерашней ссорой за ужином.

Difference:

Original: …и мы смеялись над ней за ужином.
Uses the pronoun ней to avoid repeating вчерашняя ссора.
Your version repeats the noun phrase, which is also fine, just a bit heavier stylistically.

Pronouns like ей / им / ей / ним / ней are very common in Russian precisely to avoid such repetition when the referent is clear from the previous clause.

Why is there a comma before и in …, и мы смеялись над ней за ужином?

Russian uses a comma before и when it connects two independent clauses (each with its own subject and predicate).

Here we have:

Вчерашняя ссора оказалась пустой
- subject: вчерашняя ссора
- predicate: оказалась пустой
мы смеялись над ней за ужином
- subject: мы
- predicate: смеялись над ней за ужином

Since both parts could stand as separate sentences, they are two independent clauses joined by и, so a comma is required:

Вчерашняя ссора оказалась пустой, и мы смеялись над ней за ужином.

What is the difference between ссора and спор? Both can be “argument,” right?

Both can translate as “argument,” but the nuance differs:

ссора – a quarrel, a conflict with stronger emotion, often angry, personal, with hurt feelings.
- семейная ссора – family quarrel
- у нас была ужасная ссора – we had a terrible fight
спор – a dispute / debate, can be more rational, about opinions, may be calm or emotional, but not necessarily a “fight.”
- научный спор – scientific debate
- спор о политике – political argument

In your sentence, the idea is “yesterday’s fight/quarrel turned out to be pointless,” so ссора is the natural choice.