My wife has had an Alzheimer's diagnosis since 2014. I have been giving her showers since 2018 but it is becoming more difficult. Advice?

Do you have one of those big plastic chairs like PC pipe material? If so, there are smaller ones with or without backs.

My mom has a hospital bed since her stroke so it’s a lot easier when you can elevate and lower the bed etc.
We use medline extrasorb pads under her for incontinence so I put an additional one under her back to absorb any water and keep her sheets and mattress dry while washing up.

I use a tub and basin and I use the no rinse aloevesta but I also use a Johnson and Johnson baby wash (as it’s delicate) as well at times and some soft washcloths (due to incontinence I already use throwaway washcloths so I use those). There is also a bed shampoo basin (on Amazon) that I use to wash her hair in bed or even in her wheelchair outdoors in the summer. It’s just blows up and can lay on the bed allowing you to wash her hair in bed or a chair/ table.
You can google washing or bathing from bed YouTube video - watching a few may help give you some ideas for your set up and loved one. I watched many of these before I took my mom home after her stroke and they did help me figure out what would work best for us.

I don’t know how others do it but here is how I did it with mom once my daughter and I could no longer physically help her get in the shower, onto the shower chair, and she was no longer able to help. I started giving her a sponge bath right there on the toilet. I put puppy pads on the floor to catch any accidental spills.

Filled a foot tub wash basin full of warm water (I used some lightly fragrant body wash) and a hand towel. I allowed enough water to stay in the towel so that I could see it on the skin or running down the skin as I wipe. After patting dry on areas that needed it, I then followed up with a moisturizing lotion.

I did the same way for their hair once they could no longer lean over for me to wash. With mom, I had to do it all bath and dress. Her tub was close so I placed a grab bar there and used that whenever I needed to give extra attention to lower regions to make sure no scents were left behind.

I do dad the same way now with the exception I only have to wash his back. He washes all other areas and lotion himself. The only reason I don't try the shower is that he has a bad leg that I fear would give out just when we don't need it to give.

I have to help him with his shirt over his head but then everything else he can do. Yes sometimes, I touch up the butt area if he ended up with a pull-up that was soggy to make sure no odors are present.

When mom got bedridden, the same method was used but I couldn't allow as much water to stay in the hand towel.

They have so many products on the market now as the no-rinse body wash, but I have not tried.

Try turning the shower chair so that she sits facing out into the room (make up a little step if her feet dangle), that way you can do a combo sponge bath and quick rinse with the hand held shower. 4'10'' seems plenty of room to me, if the problem is that most of it walled off then replacing that with a curtain could be a better solution.

(And a daily shower isn't necessary, 2 or 3 times a week is as often as residents at a nursing home get a full bath/shower)