Hi @geppetto, your wife may have simply forgotten to shower. My husband became adverse to showering and I had to plead with him to shower. He wouldn't wash his hair so I bought the stuff they used on me in the hospital that didn't have to be rinsed and did his hair with that. A few years later he broke his hip. I had the tub taken out and a shower bed installed with lots of grab bars and a shower chair. When he came home from rehab, I found it easier to shower with him and he lost his old aversion. I asked him why he didn't want to shower before and he said he just didn't know what to do. Now when we're showering he asks me for step by step instructions.
I agree with @larryg333, it's probably best to monitor your wife in the shower at this point. You'll be there to help her when she needs it.
My mother in law was nearly 100. She didn't have dementia, but she grew to hate showers. She said that it felt like sandpaper on her skin.
At a recent caregiver's conference, the presenter emphasized that sponge baths are an alternative to showers and hygiene warrants that armpits, genitals, and for women, underbreasts need to be washed.
Take care.