What should a girl do who suffers from obsessive-compulsive disorder (OCD) regarding purity, which causes her difficulty in performing ablution (wudu), istinja (washing after using the toilet), and prayer, and doubt about the purity of discharge, and a belief that household furniture has become impure, which has affected her performance of obligatory and supererogatory prayers?

Waswasah (obsessive whispering from Satan) is one of the worst ailments, and its cure is to ignore it and pay no attention to it. So, if you doubt that something urine-like has exited, then base your action on the original state, which is that it has not exited. If you doubt that your ablution has been invalidated, then act upon certainty, which is the validity of your purification. If you doubt that something has become impure, the original state is that it remains pure. Do not perform ghusl (ritual bath) unless you are certain of the exit of semen, which necessitates ghusl. The vaginal discharges of a woman are pure according to the more preponderant opinion, so you are not required to purify your body or clothes from anything that touches them from this. If you are certain that your ablution has been invalidated, then perform ablution. If you are certain that something necessitating ghusl has exited, then perform ghusl. You are not required to purify anything unless you are certain of its impurity.