Is it permissible for a woman afflicted with leprosy in the parts of the body subject to ablution, who uses a medicinal ointment that is affected by water, to perform tayammum instead of wudu, and if permissible, when should tayammum be performed?

If a knowledgeable doctor states, or it is proven through experience, that using water impedes treatment and delays recovery, then it is permissible for the patient to perform tayammum for every prayer until recovery. However, if it only affects recovery at certain times and not others, then tayammum is permissible only at those times. Tayammum is not permissible except when there is a fear of illness, its worsening, or a delay in its cure. Once this fear subsides, the use of water becomes obligatory.