Learn Hardcore Swedish: Utsikten över sjön gör henne så nöjd att hon vill stanna hela helgen. - The view over the lake makes her so satisfied that she wants to stay the whole weekend.

In this sentence, we are talking about a specific view: the view over that lake she is looking at. Swedish usually uses the definite form in such cases, especially when:

it is clear which thing we are talking about (the view from where she is), and
the noun is the subject of the sentence.

So:

Utsikt över sjön = a view over the lake (some view, in general)
Utsikten över sjön = the view over the lake (the one she is seeing now)

Using utsikten makes the sentence sound natural and specific in Swedish.

Why is it sjön and not sjö in över sjön?

Sjö = lake (indefinite)
Sjön = the lake (definite)

Even though sjön comes after a preposition (över), Swedish still uses the definite form when a specific thing is meant. Here, we are not talking about any lake but a particular one she is looking at.

Compare:

över en sjö = over a lake (any lake)
över sjön = over the lake (the specific one in this context)

So över sjön is like saying over the lake.

What exactly does över mean in över sjön, and could I use other prepositions?

In över sjön, över means over / across / above, depending on context. Here it describes the spatial relationship between what she sees and the lake: the view stretches over or across the lake.

Other prepositions would change the meaning:

vid sjön = by the lake / at the lake
på sjön = on the lake (often used for being out on the water, e.g. in a boat)
av sjön (in this kind of phrase) would usually not be used to mean a view of the lake.

The natural way to say the view of the lake is utsikten över sjön.

Why is it henne and not hon?

Swedish, like English, has different forms for subject and object pronouns:

hon = she (subject form)
henne = her (object form)

In the sentence:

hon is the subject of the second clause: att hon vill stanna hela helgen (that she wants to stay the whole weekend).
henne is the object of gör in the first clause: gör henne så nöjd (makes her so satisfied).

You can think of it like English:

She wants to stay. → hon vill stanna
The view makes her satisfied. → utsikten gör henne nöjd

How does the structure gör henne så nöjd work grammatically?

The pattern is:

göra (to make) + object + adjective

So:

gör = makes
henne = her (object)
så nöjd = so satisfied

Together: gör henne så nöjd = makes her so satisfied.

This is a common and productive pattern in Swedish:

Det här gör mig glad. = This makes me happy.
Nyheterna gjorde oss oroliga. = The news made us worried.
Vädret gör alla trötta. = The weather makes everyone tired.

What is the nuance of nöjd here, and how is it different from glad or lycklig?

Nöjd usually means content / satisfied, often with a calm, comfortable feeling. In this sentence, the view gives her a feeling of deep contentment.

Rough differences:

nöjd: content, satisfied, pleased with something (calm, often not very intense)
glad: happy, cheerful, in a good mood (more emotional, outward)
lycklig: very happy, fortunate, often stronger and deeper than glad

So:

Hon är nöjd med utsikten. = She is content / satisfied with the view.
Hon är glad. = She is happy / cheerful.
Hon är lycklig. = She is (deeply) happy.

Here nöjd fits well because the view makes her feel peacefully pleased and content, so much that she wants to stay longer.

What does the pattern så … att express in så nöjd att hon vill stanna?

The pattern så … att means so … that and introduces a result:

så nöjd = so satisfied
att hon vill stanna hela helgen = that she wants to stay the whole weekend

So it means:

She is so satisfied that she wants to stay the whole weekend.

Grammar-wise:

så modifies the adjective (nöjd).
att introduces a subordinate clause expressing the consequence or result.

What is the word order inside the att-clause att hon vill stanna hela helgen?

In Swedish att-clauses (subordinate clauses), the normal order is:

subject – verb – (objects/adverbs/etc.)

So:

hon (subject)
vill (verb)
stanna hela helgen (verb complement / rest of the clause)

That is why it is att hon vill stanna hela helgen, not att vill hon stanna hela helgen.

This contrasts with many main clauses, where Swedish is typically verb-second (V2), for example:

I helgen vill hon stanna. (Verb in second position)
But: Hon säger att hon vill stanna. (In the att-clause, subject comes before the verb)

Why are gör and vill in the present tense, when the staying is about the future weekend?

Swedish often uses the present tense to talk about future events when the future time is clear from context or from a time expression.

Here:

gör (makes) describes what the view is doing now.
vill stanna hela helgen (wants to stay the whole weekend) expresses her current wish about the coming weekend.

Even though stanna hela helgen is in the future, Swedish does not need a special future tense. The present tense is enough because hela helgen makes it clear we are talking about that upcoming time period.

A similar pattern:

Jag åker till Stockholm imorgon. = I am going / will go to Stockholm tomorrow.
Present tense, but clearly future from imorgon.

Why is it hela helgen and not hela helg or just helgen?

Breakdown:

helg = weekend / holiday (indefinite)
helgen = the weekend (definite)
hel = whole (adjective)
hela = whole (inflected form, used before a definite noun here)

The structure is:

hela + helgen → hela helgen = the whole weekend / all weekend

You cannot say hela helg in this meaning; you need the definite form helgen after hela when you are specifying a particular weekend.

So:

helgen = the weekend
hela helgen = the whole weekend (all of that weekend)