Is it permissible to continue guaranteeing a usurious loan contracted to purchase a home for the family?

We understand that you guaranteed your mother for an interest-based loan and then regretted it. Your regret is proof of the sincerity of your repentance and your turning to Allah. If you can cancel the guarantee, then you must do so; otherwise, what you have done is sufficient. Advise your mother to repent from falling into usury by regretting it, seeking forgiveness, and resolving never to return to it.