Hun fortæller sin veninde om filmen i stuen.

Because sin/sit/sine is the reflexive possessive in Danish. It is used when the owner is the subject of the clause.

In Hun fortæller sin veninde ..., the subject is hun, and the friend belongs to her, so Danish uses sin.

• Hun fortæller sin veninde ... = She tells her own female friend ...
• Hun fortæller hendes veninde ... = She tells another woman’s female friend ...

This is one of the most important differences from English, since English just uses her for both meanings.

The form depends on the gender and number of the noun being possessed, not on the person who owns it.

Here the possessed noun is veninde, which is a common gender singular noun, so you use sin.

The pattern is:

• sin
  • common gender singular noun
• sit
  • neuter singular noun
• sine
  • plural noun

Examples:

• Hun elsker sin bil. = She loves her car.
• Hun elsker sit hus. = She loves her house.
• Hun elsker sine børn. = She loves her children.

Veninde specifically means a female friend.

Danish distinguishes:

• ven = male friend, or sometimes friend in a general sense depending on context
• veninde = female friend

So sin veninde means her female friend.

Because Danish fortælle does not need a separate preposition before the indirect object in this structure.

So Danish says:

• Hun fortæller sin veninde om filmen.

Literally, that is something like:

• She tells her friend about the movie.

The person receiving the information comes directly after the verb:

• fortælle nogen noget
• fortælle nogen om noget

Examples:

• Jeg fortæller ham historien. = I tell him the story.
• Jeg fortæller ham om historien. = I tell him about the story.

The preposition om means about here.

So:

• fortælle om noget = to tell about something

And filmen is the film/movie.

So:

• om filmen = about the film

This is a very common Danish pattern:

• snakke om = talk about
• læse om = read about
• fortælle om = tell about

Because Danish usually expresses the by adding a definite ending to the noun.

So:

• en film = a film
• filmen = the film

This is called the suffixed definite article.

You use den film in some special situations, for example when there is an adjective:

• den gode film = the good film

But by itself, the film is normally just filmen.

This phrase is potentially ambiguous.

i stuen usually means in the living room, and in this sentence it will most naturally be understood as describing the location of the telling:

• She is telling her friend about the film in the living room.

But depending on context, a listener might briefly wonder whether it means:

• the friend is in the living room, or
• the film in the living room

If you want to make the meaning clearer, Danish can often be rephrased. For example:

• I stuen fortæller hun sin veninde om filmen.
  This strongly suggests the telling happens in the living room.

This is normal Danish main clause word order:

• Hun = subject
• fortæller = finite verb
• sin veninde = indirect object
• om filmen = prepositional phrase
• i stuen = adverbial/prepositional phrase

So the basic pattern is:

Subject + verb + other elements

Danish main clauses normally keep the finite verb in second position. Since Hun is first, fortæller comes second.

Then Danish uses its usual V2 word order, where the finite verb still stays in second position.

So:

• Hun fortæller sin veninde om filmen i stuen. becomes
• I stuen fortæller hun sin veninde om filmen.

Notice that fortæller remains second, and hun moves after the verb.

This is very common in Danish when you want to emphasize place, time, or another element.

Fortæller is present tense.

The infinitive is:

• at fortælle = to tell

The present tense is:

• fortæller = tells / is telling

In Danish, the present tense can often correspond to either simple present or present progressive in English, depending on context.

So Hun fortæller ... can mean:

• She tells ... or
• She is telling ...

Because stue in Danish commonly means living room/lounge/parlor, not just any room.

So:

• i stuen = in the living room

If you want to say in the room more generally, Danish would usually use:

• i værelset = in the room or
• i rummet = in the room/space

So stuen is a specific kind of room.

Usually veninde means female friend, not necessarily romantic partner.

In some contexts, people might use friendship words loosely, but the normal meaning is simply female friend.

If you want to make girlfriend clearly romantic, Danish often uses other wording, depending on style and context, such as:

• kæreste = boyfriend/girlfriend/partner

So most learners should understand veninde here as female friend.