Having repented from stealing things from the house, how do I repent from lying to my mother about it?

Repentance has conditions, among them: abandoning the sin, resolving not to return to it, and regretting having committed it. If the sin involves the right of another human being, then the right must be restored to him or his forgiveness sought. If informing him is impossible, then it suffices to return the stolen item or its value. One may use allusions and circumlocutions without outright lying, except in cases of extreme necessity.