Sie hat ihre Adresse hinterlassen.

Because of the verb hat.

German Sie can mean:

• she
• they
• formal you

But:

• she has = sie hat
• they have = sie haben
• formal you have = Sie haben

So Sie hat can only mean she has.

This is the present perfect tense, which is very common in spoken German.

It is built like this:

subject + auxiliary verb + past participle

So here:

• Sie = subject
• hat = auxiliary verb from haben
• hinterlassen = past participle

Literally, it works like She has left her address. In everyday German, this form is often used where English might simply say She left her address.

In a normal German main clause, the finite verb goes in the second position. Here, that finite verb is hat.

The past participle usually goes to the end of the clause.

So the structure is:

Sie | hat | ihre Adresse hinterlassen

This is standard German word order for the perfect tense.

The infinitive, or dictionary form, is hinterlassen, meaning to leave behind, to leave, or in this kind of context, to leave/give one’s address.

Its principal forms are:

• hinterlassen — infinitive
• hinterlässt — present tense
• hinterließ — simple past
• hinterlassen — past participle

So:

• Sie hinterlässt ihre Adresse. = She leaves/is leaving her address.
• Sie hinterließ ihre Adresse. = She left her address.
• Sie hat ihre Adresse hinterlassen. = She has left / left her address.

Because hinterlassen is an inseparable-prefix verb.

Many German verbs with inseparable prefixes do not add ge- in the past participle.

So:

• hinterlassen → hat hinterlassen
• not hat gehinterlassen

This also shows that the verb is not split in the present tense:

• Sie hinterlässt ihre Adresse.
• not Sie lässt ihre Adresse hinter.

Most German verbs form the perfect tense with haben.

Verbs usually take sein if they describe:

• movement from one place to another
• a change of state
• or are a few special intransitive verbs like sein, werden, bleiben

hinterlassen takes a direct object (ihre Adresse), so it is a transitive verb, and transitive verbs normally use haben:

• Sie hat ihre Adresse hinterlassen.

Not:

• Sie ist ihre Adresse hinterlassen.

Here, ihre means her.

It is the possessive determiner agreeing with Adresse:

• Adresse is feminine singular
• so the form is ihre

A useful detail: ihre could also mean their in other contexts, but here the most natural reading is her.

It does not mean formal your here, because formal possessives are capitalized:

• Ihre Adresse = your address (formal)
• ihre Adresse = her address or their address

Because a possessive determiner like ihr-/ihre works in the same slot as an article.

So you say:

• die Adresse = the address
• ihre Adresse = her address

You do not normally use both together:

• not ihre die Adresse

The possessive word is already doing the job of introducing the noun.

It is in the accusative case, because it is the direct object of hinterlassen.

You can ask:

• Was hat sie hinterlassen?
• Ihre Adresse.

Since Adresse is feminine singular, the accusative looks the same as the nominative here:

• die Adresse (nominative)
• die Adresse (accusative)

That is why the noun itself does not change visibly.

Because it has to agree with the gender, number, and case of the noun it goes with.

Here:

• Adresse is feminine
• singular
• accusative

With a feminine singular accusative noun, the possessive determiner takes -e:

• ihre Adresse

Compare:

• ihr Bruder = her brother
• ihre Schwester = her sister
• ihr Kind = her child
• ihre Freunde = her friends

Yes. The simple past version is:

Sie hinterließ ihre Adresse.

That means the same thing in most contexts.

Difference in usage:

• Sie hat ihre Adresse hinterlassen. → very common in speech
• Sie hinterließ ihre Adresse. → more common in writing, storytelling, or formal narration

So as a learner, the perfect tense version is especially useful for everyday conversation.

They are related-looking verbs, but they mean different things.

• hinterlassen = to leave behind, to leave something
• verlassen = to leave a place or person

Examples:

• Sie hat ihre Adresse hinterlassen. = She left her address.
• Sie hat das Haus verlassen. = She left the house.
• Er hat sie verlassen. = He left her.

So in your sentence, hinterlassen is the correct verb because the idea is that she left something behind: her address.