That you didn't get xp is the warranted punishment for letting such a dangerous and extremely evil monster live and continue with torturing and killing innocent people just for her pleasure.
In earnest, I concur with you, the party should technically achieve the same amount of xp for any valid solution of a situation. I always kill the hag and never ever would take her hair and let her go even if she would not take the woman with her. But there is the surrender of the hag as a dialog option, why is it so difficult to give xp after the dialog? They did it in other situations, why not here? In the windmill fight you got no xp shortly after EA release if you did not kill the goblins. Now you get the xp also if you accept surrender of the boss.
