I find the translation "You girls have changed". So is fetelor here genetive in the sense of "You of the girls" ?
Nope, fetelor is vocative here.
Plural vocative can take the definite genitive-dative plural form (the -lor one) of the noun.
And the proper punctuation is actually: Voi
, fetelor, v-aţi schimbat (the noun in vocative has to be separated from the rest of the sentence by commas).
Thank you, with that extra comma I probably could have figured it out myself. Did some Latin for a reason, about 35 years ago :-)