This "the witch killed and took Inase form" seems like a cover story to me, instead of actual facts. (that maybe the father created to protect himself and his family)
Frist of all becouse we aren't showed what happened, we aren't even showed the "real" body (that should be present somewhere)
Secondly becouse the girl in the beginning seemed actually terrorized with the prince actions and the tree reactions, even screaming to the prince to save her. Also He in the begininng was saying he had something to check, so he bringed her to the tree.
Even admitting se was a witch, there were no proof of any wrongdoings of her.
So no, this can't be considered for now reliable informations until more is revealed, and not enough to absolve the prince.