У неё была такая маленькая сумочка, что туда не вошёл даже зонт.

Russian usually expresses possession with the pattern у + genitive + есть / был / была / было.

So:

• У неё была сумочка = literally At her there was a little bag
• Natural English: She had a little bag

This is much more normal in everyday Russian than using иметь (to have).
The verb иметь does exist, but it often sounds more formal, bookish, or emphatic.

Because у requires the genitive case.

The pronoun она changes like this:

• nominative: она = she
• genitive: её / неё = of her / at her

After many prepositions, Russian uses the н- form of third-person pronouns:

• у неё
• к нему
• с ними

So у неё means at her / with her / she had depending on context.

Because the thing being talked about is сумочка, and сумочка is feminine singular.

In the Russian possession structure, the possessed thing behaves grammatically like the subject:

• У неё была сумочка
• literally: At her was a little bag

Since сумочка is feminine, the past-tense verb is feminine too:

• был = masculine
• была = feminine
• было = neuter
• были = plural

Сумочка is a diminutive form of сумка.

• сумка = bag
• сумочка = little bag, handbag, purse, or just a more affectionate/smaller-sounding bag

Diminutives in Russian often suggest one or more of these:

• small size
• affection
• softness
• informality

So here сумочка helps create the idea of a small handbag/purse.

This is a very common Russian pattern meaning so ... that ...

In this sentence:

• такая маленькая сумочка, что...
• such a small little bag that...
• more natural English: a bag so small that...

Structure:

• такой / такая / такое / такие
  • adjective/noun
• then что = that

Examples:

• Он был такой уставший, что сразу уснул.
  He was so tired that he fell asleep immediately.
• Это была такая трудная задача, что никто не решил её быстро.
  It was such a difficult task that nobody solved it quickly.

Because all the words have to agree with сумочка, which is:

• feminine
• singular
• nominative

So:

• такая = feminine singular nominative
• маленькая = feminine singular nominative
• сумочка = feminine singular nominative

They all match.

If the noun were masculine, you would get:

• такой маленький зонт

If plural:

• такие маленькие сумочки

Because что introduces a subordinate clause here.

Main clause:

• У неё была такая маленькая сумочка

Subordinate result clause:

• что туда не вошёл даже зонт

Russian normally separates this kind of clause with a comma.

This is very similar to English so... that..., where English also often uses a clause break:

• She had such a small bag, that...
  In natural English the comma is often omitted, but in Russian the comma is standard.

Туда means there, into there, to that place and usually implies direction.

Там means there in the sense of location.

Here the idea is that the umbrella could not go into the bag, so Russian uses туда:

• туда не вошёл зонт = the umbrella didn’t go in there / didn’t fit in there

Compare:

• там лежит зонт = the umbrella is lying there
  location
• зонт туда не вошёл = the umbrella didn’t go in there
  movement/direction

Войти / входить literally means to go in / enter.

Here вошёл is the past tense of the perfective verb войти, and in this context it means something like:

• didn’t go in
• didn’t fit in

So туда не вошёл даже зонт literally means:

• even an umbrella did not go in there

Natural English:

• even an umbrella wouldn’t fit in it

Russian often uses verbs of movement in places where English prefers fit.

Because the grammatical subject is зонт, and зонт is masculine.

So the past tense must be masculine singular:

• зонт вошёл
• книга вошла
• письмо вошло
• вещи вошли

Even though зонт comes after the verb, it is still the subject.

Because зонт is the subject of the verb вошёл.

Russian negation does not automatically force every noun into the genitive. Here the structure is:

• зонт не вошёл
• the umbrella did not go in

Since зонт is the one performing the action grammatically, it stays in the nominative.

This is different from some negated direct objects, where Russian may use the genitive:

• Я не вижу зонта = I don’t see an umbrella / the umbrella

But here зонт is not a direct object.

Даже means even.

It adds emphasis: not only did larger things not fit, but even an umbrella did not fit.

So:

• туда не вошёл даже зонт
• even an umbrella didn’t fit in there

Its position is flexible, but here it directly highlights зонт.

Compare:

• Даже зонт туда не вошёл = Even an umbrella didn’t fit in there
• Туда не вошёл даже зонт = similar meaning, with a slightly different focus and rhythm

Yes, в неё would also be possible:

• ...что в неё не вошёл даже зонт

That means more explicitly:

• ...that even an umbrella didn’t fit into it

The version with туда sounds a bit lighter and more natural in narrative speech, because the bag has already been mentioned and туда can simply mean in there.

So both are possible, but:

• туда = more adverbial, in there
• в неё = more explicit, into it

Russian word order is flexible, and it often reflects information structure rather than fixed grammar rules.

In:

• туда не вошёл даже зонт

the sentence builds toward зонт at the end, which gives it emphasis. It is almost like a punchline:

• the bag was so small that in there didn’t fit even... an umbrella

You could also say:

• Даже зонт туда не вошёл
• Зонт туда даже не вошёл

These are grammatical, but the original order sounds natural and expressive.

It is the same basic word form, but here it means that, not what.

Russian что can mean different things depending on context:

• Что это? = What is this?
• Я знаю, что он дома. = I know that he is at home.
• ...такая маленькая сумочка, что... = ...such a small bag that...

So in this sentence, что introduces the result clause: that even an umbrella didn’t fit in there.