"You are not a woman but a girl!"
Translation:Nejsi žena, ale holka!
It does not make much sense in Czech.
If you wanted to stress and contrast the verb, you could do
Žena nejsi, ale dívka jsi. Žena nejsi, ale dívka ano.
but then the meaning is very different. *You are not a woman, but you are a girl. *
But if you just contrast "not a woman but a girl", then keep thee words together "(ne) žena, ale dívka".