Η φίλη μου φόρεσε μωβ μπλούζα στο πάρτι.

Because Greek normally uses the definite article with possessive words like μου, σου, του, etc.

So:

• η φίλη μου = my friend
• το σπίτι μου = my house
• ο αδερφός της = her brother

In English, the disappears in this structure, but in Greek it usually stays.

Without the article, φίλη μου can sound like direct address, emotional speech, or a less neutral style, depending on context.

In normal Greek, the weak possessive form μου usually comes after the noun:

• η φίλη μου
• το βιβλίο μου
• η μητέρα μου

This is the standard pattern.

If you want strong emphasis on my, Greek often uses δικός/δική/δικό instead:

• η δική μου φίλη = my own friend / my friend with emphasis

So η φίλη μου is the normal, neutral way to say it.

Yes. φίλη is feminine singular, so it refers to a female friend.

Compare:

• η φίλη μου = my female friend
• ο φίλος μου = my male friend

English friend does not show gender, but Greek usually does.

φόρεσε is the aorist form, 3rd person singular, of φοράω / φορώ.

Here it means a single completed action in the past.

So:

• φοράει = she wears / she is wearing
• φορούσε = she was wearing / used to wear
• φόρεσε = she wore / she put on

The aorist is one of the most common past tenses in Greek.

It can mean either, depending on context.

With clothing verbs, Greek φοράω and its forms can cover both ideas:

• to wear
• to put on

In this sentence, English usually prefers wore, because the sentence is describing what she had on at the party.

So:

• Η φίλη μου φόρεσε μωβ μπλούζα στο πάρτι. naturally becomes
• My friend wore a purple blouse to/at the party.

But in another context, put on could also be a good translation.

Because Greek often omits the indefinite article where English would use a/an.

So both of these are possible:

• φόρεσε μωβ μπλούζα
• φόρεσε μια μωβ μπλούζα

The version without μια is very natural.
The version with μια can sound a bit more specific, a bit more explicit, or just slightly fuller.

This is a common difference between Greek and English:

• Greek uses the definite article more often than English.
• Greek uses the indefinite article less often than English.

Because μωβ is an indeclinable color word.

That means it stays the same no matter what noun it describes:

• μωβ μπλούζα = purple blouse
• μωβ πουκάμισο = purple shirt
• μωβ παπούτσια = purple shoes

Many color words borrowed from other languages behave like this in Greek, such as:

• ροζ
• μωβ
• μπεζ

So unlike a regular adjective, μωβ does not change for gender, number, or case.

It is the object of the verb, so grammatically it is in the accusative.

However, many feminine nouns ending in -α look the same in the nominative and accusative singular.

For example:

• η μπλούζα = the blouse, as subject
• τη μπλούζα = the blouse, as object

The noun itself stays μπλούζα.
What often shows the case is the article:

• nominative: η
• accusative: τη(ν)

In your sentence, there is no article before μπλούζα, so the noun form looks unchanged.

στο is a contraction of:

• σε + το = στο

This is extremely common in Greek.

The preposition σε with the accusative can mean:

• to
• in
• at depending on the context.

So:

• στο σπίτι = to the house / at home / in the house, depending on context
• στο πάρτι = at the party

In this sentence, at the party is the most natural interpretation.

πάρτι is a borrowed word, and in Greek it is treated as a neuter noun:

• το πάρτι

It is also usually indeclinable, which means the noun itself does not change form in different cases.

So you may see:

• το πάρτι
• στο πάρτι
• από το πάρτι

The article and preposition do the grammatical work, while πάρτι stays the same.

Greek word order is more flexible than English word order.

The given sentence:

• Η φίλη μου φόρεσε μωβ μπλούζα στο πάρτι.

is a very natural, neutral order:

• subject
• verb
• object
• prepositional phrase

But Greek can move things around for emphasis, topic, or style. For example:

• Στο πάρτι η φίλη μου φόρεσε μωβ μπλούζα.
• Μωβ μπλούζα φόρεσε η φίλη μου στο πάρτι.

These are still grammatical, but they place emphasis on different parts of the sentence.

For learners, the original version is the safest and most neutral pattern.