Are we sure that's her original head?! Any markings or anything? Never seen one so closely related to a Barbie doll before, but I am no expert and I guess stranger things have happened. Fakies/imitations are probably better quality today anyway than when I was a kid. Because your doll has the white underpants, she must be a pretty recent copy though, right? When did Barbie start having white painted-on undies?
I keep coming back to look at her face; I get this feeling that she was intended to look like a well-known character, celebrity, or real-life personality. The fact that she doesn't have the full-on 'Barbie smile', like most fashion dolls, and has oddly shaped down-turned eyebrows that convey a whole new expression or personality makes me wonder. For some reason her face is familiar. Anyone else sensing that?
I thought she might be the Elizabeth doll from the Sweet Valley High series, or Stacey from BSC series, because they had a closed mouth too, but it's not. This doll's face is pretty narrow as well, which is unusual to me. Could it be an older Disney Princess doll or something, like Sleeping Beauty? A foreign line? No idea.