Alternative bathing/ shower options?

Agree with others *Sponge bath*, *top & tail* or *sweet spots*. Whatever you call it - a sink/basin, a wash cloth, soap & water.

I find a wetting, then a soapy washer, then a water only washer rinse is the way to go - no soap left on to get itchy. Hair is harder but same idea.

I can't see any realistic option other than some variation of sponge baths; either using the bathroom sink, a basin or disposable towelettes. For her hair there are dry shampoos and no rinse shampoos, but if she is able a trip to the salon might be a nice treat.

I just returned from visiting my 98-yr old aunt who is recovering at home with a broken knee cap. She's in a velcro cast and wheelchair (she has late stage dementia as well). The caretake has her washing up near the kitchen sink, as in sponge bathing, and has her sit on a portable potty chair to clean her "netherlands". They put down some large beach towels to keep the floor dry and safe. If your MIL is able to stand for a short time and bend over, she can also wash her hair in the same sink (hopefully you have a hand-held spray function on the faucet). Special non-water-and-soap based products are available for those who cannot really bath (like for the bedridden in nursing homes) but they might not please your MIL. This may not be the best option but it is all we can do at my Aunt's residence. I'm sure others will soon post some clever suggestions for your MIL.