For starters, avoid using soap when you wash your mother, because it's drying and can cause her skin to crack, which could lead to pressure sores. Soap depletes skin of
oils that protect against skin breakdown.
To keep your mother's skin in good shape, use a soft disposable washcloth, as most fabric washcloths are hard on fragile skin. Look for the type that comes with built-in, no-rinse cleansers. Be sure to wash her genital area from front to back to keep her clean and prevent the spread of bacteria. After you've cleaned her and gently patted her dry, put on a moisturizer, and then a barrier that protects the skin against urine and stool. Comfort Shield is one brand, but almost any barrier that contains petrolatum, zinc oxide, or dimethicone should work. Some products include both moisturizers and barriers, and those are fine as well. To be extra safe, during her next office visit ask your mother's doctor to recommend specific brands for her.
It's also important to change your mother's underwear or adult diapers regularly, so she doesn't sit in soiled or wet diapers. Stool and urine can break down the skin, causing painful pressure sores and yeast rashes.