You both should have received specific instructions from the home dialysis nurse about cleaning the exit site, either for hemo or PD. So please, check with the nurse to see what the clinic protocols are. That said, for the PD catheter, it is usually recommended that the PD catheter not be disturbed during the first week after the surgery to implant the catheter. This allows the tissue around the exit site to heal. Generally an absorbent dressing is applied in the operating room which is to be removed only by the PD nurse using sterile technique either at the end of 5-7 days or whenever the dressing is wet with blood or fluid. Patients are instructed not to shower or bathe for the first week. After this initial healing, a small dry dressing is placed over the exit to anchor the catheter and keep the area clean. At this point, most recommend application of a small amount of either mupirocin or gentamicin daily after thorough cleaning and drying (and all this is to be taught to the patient by the nurse). Your question about whether daily exit site care should be done in the bathroom is a good one. It should be fine to do this in the bathroom however the procedure will always be started with thorough washing and drying of hands. Many patients are allowed to wash their exit site in the shower daily (once the nurse has told you the area is healed) with again, thorough drying around the site. Some bacteria grow readily in water so it is very important that the exit site is dried after cleaning. The goal is to have the PD catheter exit site heal without infection and keep it free from future infection by keeping the catheter anchored (so it does not pull on the exit site), keeping it clean and dry, and applying preventive antibiotics either at the exit site or by applying mupirocin to the nose for 5 days every month.
Since your Mother also has a hemo catheter, the cleaning should be done by the nurses who put her on hemo in center. Home care of this site should be directed by the hemo nurses. Remember that this catheter has a direct access to blood, so keeping it free of infection is also quite important as this can result in a very serious infection.
Good luck to you both on your home therapies.