Elliot is manipulative af (very sus tbh). The Mom didn't show any negative emotions towards mc (could be too early to tell) and even spoke positively of her father. There is a possibility that Elliot is the actual kidnapper...
More than likely her father, because in one of the earlier chapters I vaguely remember him thinking about some strange dreams he's been having about MC's execution, his deep regret, and a spell he took part in.