I don’t think the wizard is her father. If you pay attention to the first season with the original curse, it requires the heart of the thing you love the most which is why Regina chose her father. From what we know Zelena did not have that connection with either her real dad or her adoptive.
personally I’m hoping its rumple that way she would technically be his Second born and Belle will be able to keep her child but at this point who knows. Plus I’d love to see her back in this season