Thank you for taking on the task of speaking to your sister. She obviously needs someone to help her and give her advice and information. Not wiping will cause irritation and soreness which could lead to infection. Just think what a baby's bottom looks like after sitting in a wet diaper. It's not a healthy environment. Be sure to remind her also to wipe from front to back so as not to spread bacteria from the rectal area to the vaginal area. Also, not wiping leads to odor. No one wants to smell like pee. I hope this helps. Good luck.