All praise be to Allah Alone, and peace and blessings be upon His Messenger, and his family and Companions.
It is Haram to put tattoo on any part of the body whether it is full or not. Your mother must remove this tattoo if doing so will not cause her any harm. She should also make Tawbah (repentance to Allah) and Istighfar (seeking forgiveness from Allah) for what she has done in the past.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.