All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon Prophet Mohammad and upon all his family and companions.
It is impermissible to remove an organ that has been created by Allah the Almighty except in situations where such a procedure is required. As for mental disability and failure to control one`s actions, this isn`t a legitimate excuse that permits operating on this child. The latter represents an act of transgression against Allah`s creation as well as a health risk. Parents and guardians of this child should monitor her actions to keep her out of harm's way.
We (Iftaa` Department) advise you (Parents) to exercise patience, seek reward from Allah for taking care of this child, and ask Him to admit you to Janah for that. We also recommend that you seek the assistance of charitable associations and social institutions specialized in the affairs of such children. And Allah is the One Whose Help is sought and He The Almighty Knows Best.