My mother, who is 103, had a sit down shower installed a few years ago. It has 2 shower heads, one of them being a hand held mounted about waist height. She can sit on a stool and use it to wash all over. Make sure the stool has a back to keep an elderly person from rolling off backwards.

This one is one I installed for my MIL who used to live with us. The hand held slides up and down the bar so a person can sit on a stool and reach it.
[Linked Image from i.imgur.com]

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