"She is a girl, and he is a boy."
Translation:Ő lány, ő pedig fiú.
"Ő egy lány, ő pedig egy fiú" is correct. "van" is omitted in Hungarian unless there's an adverb or something like that. Not sure how the rule goes.
Also, if you put "pedig" first, it means something like "although". "Megbuktam, pedig tanultam." (I failed although I studied.)
To be precise, pedig does not only mean although - that is only one meaning.
It can also mean "and":
Ő egy lány, ő pedig egy fiú
She is a girl and he is a boy.
Ez az enyém, ez pedig a tiéd. or Ez az enyém ez meg a tied.
This is mine, and this is yours.
I said that's what it meant if you put it first in the clause because that's the mistake she made.
Firstly, it's Ő, not Ö. Secondly, if you put "van" in the first clause, it is better to put it in the second clause too. Also, since the word order in Hungarian is free, there are lots of different versions of one sentence, it's really hard to add them all during development stage.