None of them is dative. You are right, "friends" are the subject, the first "her" defines it - whose friends? her friends, not his or mine. The last "her" is the object for the verb "heard" - whom didn't they hear? her, not me or themselves. Both "her"s are different forms of the pronoun "she", though they look the same in both Ukrainian and English. This is not the case, eg., for German: ihre Freunde hörten sie nicht (ihre and sie are the forms used in our sentence, but they don't look the same anymore). Or French: ses amis ne l'écoutaitent pas (ses and l'). Hope this was helpful.