Ей подходит почти какой угодно шарф, потому что у неё светлая куртка.

Because подходить in the meaning to suit / to go well with someone takes the person in the dative case.

• она = she (nominative)
• ей = to her / for her (dative)

So:

• Ей подходит шарф = The scarf suits her

Russian structures this differently from English. The scarf is the thing doing the “suiting,” and her is the person it suits.

Russian often uses the singular when speaking about a general class of things.

• почти какой угодно шарф literally means almost any scarf
• In natural English, we might also say almost any scarf rather than almost any scarves

So the singular here is completely normal and means any individual scarf of that type.

Here подходит does not mean is coming / is approaching. It means:

• suits
• matches
• goes well with

The verb is подходить.

Compare:

• Поезд подходит к станции = The train is approaching the station
• Этот цвет тебе подходит = This color suits you

In your sentence, it means that a scarf looks good with her jacket / appearance.

Какой угодно means any whatsoever, whichever you like, or simply any in a very broad sense.

So:

• какой угодно шарф = any scarf at all

With почти, it becomes:

• почти какой угодно шарф = almost any scarf

This expression is very common in Russian and emphasizes that the choice is wide and not limited much.

They are often similar, and in this sentence любой would work too:

• Ей подходит почти любой шарф

But there is a slight nuance:

• любой = any / every
• какой угодно = any at all / whichever one you want

Какой угодно can sound a bit more emphatic or freer in choice. In this sentence, both are natural.

Because почти modifies the whole idea of any scarf.

• почти какой угодно шарф = almost any scarf

It means that not literally every scarf suits her, but the number of suitable scarves is very large.

If you move почти, the sentence can start to sound awkward or change emphasis.

Russian usually expresses possession with у + genitive + есть / implied “is” rather than with a verb like to have.

So:

• у неё светлая куртка = literally at her, there is a light jacket
• natural English: she has a light-colored jacket

Russian иметь exists, but in everyday speech it is much less common for ordinary possession.

After prepositions, third-person pronouns usually gain an initial н-.

So:

• её = her
• but after a preposition: у неё, для неё, с неё, etc.

This is a standard rule:

• у него
• у неё
• у них

So у её is incorrect here.

Because in у неё светлая куртка, the thing possessed is in the nominative case.

The structure is:

• у неё = she has
• светлая куртка = the item she has

So куртка stays nominative, and the adjective matches it:

• светлая куртка = nominative singular feminine

You would get светлую куртку only if the noun were a direct object, for example:

• Я вижу светлую куртку = I see a light-colored jacket

Because it agrees with куртка, and куртка is a feminine noun.

Agreement in Russian means the adjective matches the noun in:

• gender
• number
• case

So:

• светлая куртка — feminine singular nominative
• светлый шарф — masculine singular nominative
• светлое пальто — neuter singular nominative

Here it means light-colored jacket, not necessarily bright in the sense of vivid or flashy.

Светлый often means:

• light in color
• pale
• fair

So светлая куртка suggests a jacket in a pale or light shade, which makes many scarves match it well.

Because they are in different grammatical cases and roles.

• ей = dative, used with подходит
• неё = genitive after the preposition у

So in the same sentence:

• Ей подходит... = It suits her
• у неё... = she has...

This is very normal in Russian: pronouns change form depending on their function in the sentence.

Yes. Russian word order is flexible, though the emphasis changes.

For example, these are all possible:

• Ей подходит почти какой угодно шарф, потому что у неё светлая куртка.
• Почти какой угодно шарф ей подходит, потому что у неё светлая куртка.
• Потому что у неё светлая куртка, ей подходит почти какой угодно шарф.

The original version is neutral and natural. Moving words around usually changes what is emphasized rather than the basic meaning.

Because its subject is шарф, which is singular masculine.

Russian verbs in the present tense agree with the subject in number (and in the past tense, also gender).

Here:

• шарф = singular
• so подходит = singular

If the subject were plural:

• Ей подходят почти какие угодно шарфы = Almost any scarves suit her

Yes. Потому что is the standard, very common way to say because.

So:

• ..., потому что у неё светлая куртка = ..., because she has a light-colored jacket

In everyday Russian, this is the most common choice. There are other ways to express cause, but потому что is the most straightforward here.