My 93 year old mom does not take showers regularly like she used to. She gets mad when I ask her to take a shower which she is physically able to do. She told me this morning that no one had to tell her when to take a shower. I believe the last time she took one was 6 days ago. I don't know what to do.
If so, for a tub there's a product (awesome, by the way) that the tub edge gets cut down and this piece inserted over the cutout that lets a bather open the little door to easily step through but the little door seals the edge so the tub can still be used as a bathtub. If you're not able to, then hire a plumber to install grab bars or a handyman/woman to redo the shower floor so it's not slick.
Also impress on your mom that bathing every few days has many benefits. It prevents skin breakdown, helps her skin stay intact, allows her or a bath aid to ensure her skin is in good condition or stop any irritation or breakdown early, and it's so relaxing.
We also need to realize that someone in their 80's or 90's, that taking a shower is very exhausting, it's like being at the gym for an hour. I know I and my sig other are starting to feel that way at our age :P Baby wipes come in very handy.
And there are cases where some elders become claustrophobic being in the shower, and that can become very scary.
When my Dad got older, he had grab bars installed in the bathtub/shower by a plumber. Later we got Dad a bath chair which made him feel more secure. And don't forget to have a bathmat inside the tub [for some strange reason, bathmats aren't as easy to find as years ago].