It is not permissible for one of the parents to single out some of his children for a gift. They should treat them justly without discrimination. The Prophet (peace be upon him) said:
Fear Allah and treat your children justly.
He (peace be upon him) said so after he had condemned the acts of the Companion who singled out some of his children for a gift. Your mother's act was not permissible, so you have to give it back and distribute the house according to the legal way of inheritance; the male takes the share of two females. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.