"The girl has skirts."
Translation:Kızın etekleri var.
We don't have a "have" in Turkish. The above sentence has no verb. No verb no cry-ehmm-no accusative.
Var = is/are existant.
So we say: The girl's skirts are existant.
etek (skirt) → etekler (skirts) → etekleri (her skirts)
P.S.: If it's going to be of any comfort to you, the accusative would have been "etekleri" as well. So good job on that!