"Is she her friend?"
Translation:Ist sie ihre Freundin?
"Ist sie ihre Freund?" is grammatically wrong. "Freund" is a masculine noun. If you want to use "Freund" instead of "Freundin", you have to use a masculine possessive article: "Ist sie ihr Freund?". However, since we're talking about a girl ("she"), using the word "Freundin" (female friend) would be better.
Still Freund! My understanding is that context is meant to help distinguish between just a friend or something more, though I'm no native speaker.
In the same way, "Freundin" can mean friend and girlfriend. I guess kind of like how "Mann" and "Frau" can be man/ husband and woman/ wife respectively
Unfortunately this is one of the cases where knowledge of the nature of the objects in the sentence only confuses and should be ignored.
Regardless of the fact that we know the Freund is a she, use of 'Freund' instead of 'Freundin' means the article has to match the fact that Freund is a masculine noun.
Consider the following lyric from the Rammstein song 'Sonne':
"Sie ist der hellste Stern von allen."
"She is the brightest star of all."
The object is a she, but the noun is Stern, which is a masculine noun, so the article must be 'der'. It doesn't matter if 'she' is a bus, a plane, a star, a cheesecake, or a friend - the article must match the noun.
As far as I'm aware, 'Freundin', unlike other female mutations of nouns such as 'Lehrerin', 'Kanzlerin', etc., doesn't just mean a friend who is female, instead meaning specifically 'girlfriend'. I've quizzed a few Germans on this and they struggle to explain it, only saying that if you mean a friend who is female you use 'eine Freundin von mir' but that with Freund the opposite is true: 'Freund' by default is a friend, and to specify a boyfriend you qualify it with, for example 'fest' as the adjective, or with a possessive such as 'mein'. In either case, qualifying with 'fest' or a possessive indicates a boyfriend/girlfriend, while using 'ein(e) ... von mir' indicates just a friend.
When does 'sie' mean 'hers'? I don't think that's right.
If you were to say 'Is it hers?', you'd have to say 'Ist es ihres?'. You might colloquially be able to get away with 'Ist es ihrs?' but I'm not certain on that.
Regardless, 'hers' is not correct for this sentence; only 'her', which as an adjective is always 'ihrer/ihre/ihres/etc'.
Her as the direct object is 'sie', the same as the subject. In this sentence, there is only the subject, twice: once as 'she' (sie) and once as 'her friend' (ihre Freundin). In the same way, the sentence 'Er ist der Held' (He is the hero) has the subject twice: once as 'er' and once as 'der Held', which is why the case for hero is nominative: 'der Held' and not 'den Held'.
Ah, yes. In 'Ich liebe sie', 'sie' is the direct object (accusative), whereas in this sentence we're looking for 'ihr' because we need the possessive pronoun (aka the determiner) to describe the friend.
'Ist sie eine Freund von sie' must be either 'Ist sie ein Freund von ihr' or 'Ist sie eine Freundin von ihr'. 'von' is a dative preposition, so we have to shift the accusative 'sie' into the dative 'ihr'. You can pick whichever you like between Freund and Freundin but the gender of the article must match the gender of the noun: ein Freund (m) or eine Freundin (f).
The dative/accusative status of prepositions can be referenced here: https://en.wikibooks.org/wiki/German/Grammar/Prepositions_and_Postpositions