What should one who suffers from obsessive-compulsive disorder concerning purity and prayer do when she finds a recurring movement in the anus during prayer and feels air bubbles in the anus? Should she interrupt her prayer and repeat her ablution and prayer?

The cure for obsessive whispers (waswas) is to turn away from them and ignore them. You must persist in this. Do not cut short your prayer or repeat your ablution merely due to a doubt about something having exited. Rather, ablution is not invalidated except by certain and firm conviction that something has exited. The default is the validity of purity unless the contrary is proven with certainty.