Sie richtet den Kragen ihrer Bluse vor dem Spiegel.

At the beginning of a sentence, both sie and Sie are written with a capital letter, so capitalization alone does not tell you the meaning.

The verb does:

• sie richtet = she adjusts/straightens
• Sie richten = you adjust/straighten in the formal sense

Because the sentence has richtet, which is 3rd person singular, the subject must be she.

Richtet is the 3rd person singular present tense of richten.

Here, richten means something like:

• to straighten
• to adjust
• to fix

So Sie richtet den Kragen means She straightens/adjusts the collar.

This verb has other meanings in other contexts, but in a sentence about clothing, adjusts/straightens is the natural meaning.

Because den Kragen is the direct object of the verb.

The noun Kragen is masculine:

• nominative: der Kragen
• accusative: den Kragen

Since she is adjusting the collar, German uses the accusative case here:

• Sie richtet den Kragen.

A good way to think about it is:

• Who is doing the action? → Sie
• What is being adjusted? → den Kragen

Because ihrer Bluse is in the genitive case, showing possession.

den Kragen ihrer Bluse literally means:

• the collar of her blouse

In natural English, that becomes:

• her blouse collar
• the collar of her blouse

So:

• Kragen = collar
• ihrer Bluse = of her blouse

If you used ihre Bluse, that would not fit the grammar here, because the sentence is not saying she is adjusting her blouse directly. She is adjusting the collar belonging to the blouse.

It is dative.

The preposition vor is a two-way preposition, which means it can take:

• accusative for motion toward a place
• dative for location

Here the meaning is in front of the mirror, describing where she is doing the action, so German uses the dative:

• vor dem Spiegel

Compare:

• Sie steht vor dem Spiegel. = location, so dative
• Sie tritt vor den Spiegel. = movement to a position in front of the mirror, so accusative

Because Spiegel is a masculine noun: der Spiegel.

After vor with a location meaning, you need the dative, and masculine nouns take dem in the dative singular:

• nominative: der Spiegel
• dative: dem Spiegel

So:

• vor dem Spiegel = in front of the mirror

That is a very normal German word order.

The basic structure here is:

• Sie = subject
• richtet = verb
• den Kragen ihrer Bluse = object
• vor dem Spiegel = place expression

German often puts time, manner, and place information after the main object, especially in a neutral statement. So this sentence sounds natural as written.

But German word order is flexible, and you could also say:

• Vor dem Spiegel richtet sie den Kragen ihrer Bluse.

That version puts more emphasis on where the action happens. The finite verb still stays in second position.

Because vor dem Spiegel describes her physical location: she is standing in front of the mirror.

Im Spiegel would mean in the mirror, referring to what appears in the reflection.

So:

• vor dem Spiegel = where she is
• im Spiegel = what is seen in the mirror

In this sentence, the idea is that she is adjusting her collar while standing in front of the mirror, so vor dem Spiegel is the right choice.

Yes, you could.

Sie richtet sich den Kragen means She adjusts her collar, using a dative reflexive pronoun:

• sich = for herself / on herself

That version is common when the clothing item belongs to the subject.

The sentence you have, Sie richtet den Kragen ihrer Bluse, is a bit more explicit:

• it names exactly which collar
• it ties the collar directly to the blouse

So the two versions are similar, but not identical in focus:

• Sie richtet sich den Kragen. = she adjusts her own collar
• Sie richtet den Kragen ihrer Bluse. = she adjusts the collar of her blouse

By itself, yes. The form ihrer can belong to different possessive meanings depending on context, such as:

• her
• their
• formal your

But in this sentence, the natural reading is her, because the subject is she, and the whole sentence is describing what that woman is doing with her blouse.

So although the form can be ambiguous in isolation, the context makes her blouse the intended meaning here.