She is physically mature, and she can understand and enjoy sexual pleasure. We might have no right to deny her that opportunity. The fundamental issue here is whether we have a right to force the daughter to have an abortion. She would be unlikely to understand what an abortion is, and given her communication difficulties as a result of her deafness, we obviously cannot get informed consent from her. We do not have a general right to do whatever we like to incompetent people.
Legal guardians have the right to order medically necessary treatments.
But obviously parents and legal guardians do not have the right to order just any medical procedure. Parents do not have the right to make decisions to order bodily invasive procedures which are clearly against the best interests of the child. That is a form of abuse. So a major issue here is whether the abortion is in the best interests of the daughter. Even if it is, it might still not count as being medically necessary .