Walk-in shower or walk-in tub for elderly with dementia?

Geaton's comment about shivering reminded me of something else - a heater! Even a warm bathroom will feel cold to someone who is wet when the curtain is left open because someone is assisting them.

I have read from others on this forum that the walk-in tub takes a long time to fill and your LO is sitting there shivering waiting for that to happen, and then again when the tub drains because it has to drain completely first before opening the door.

I have a 99-yr old aunt with mod/adv dementia who is barely mobile but aids get her to the shower with her walker and a belt. The bathroom is very small and so is the shower, which has a 1" threshold height, but the seat is right there and the adjustable height, handheld shower head helps control the spray. Best if you get a showerhead that has all the controls on it, not the wall (on/off, temp). If modesty is an issue they can cover her with a thin terry towel, it will act like a giant washcloth and then put a dry terry robe on her right after. People who are soapy are also very slippery, so it may be safer to handle her with the help of towels during the process. Also, my aunt only needs a shower 2x a week. Those tubs are incredibly expensive and then would need to be removed when you eventually sell your home.

Even if you don't have room for a fully ADA compliant accessible bathroom you can still do a lot to enhance accessibility. My remodel included widening the door and replacing the big vanity with a smaller profile pedestal sink (I think a wall hung sink would have been better but there were time and budgetary restraints). One of the key features in a wet room is the level floor, over time even the three inch step into our low profile shower became stumbling point for my mom, and once she could no longer stand and pivot from her wheelchair it may as well have been a wall.
Don't forget lots of properly anchored grab bars. And don't let anyone talk you into a shower unit with a built in bench, they are not adequate for accessibility.

Oh... for safety and accessibility plan for a curtain not an enclosure

As for the how to - try searching shower assistance for elderly on YouTube for videos

sorry, put reply in wrong place

shower much easier

I'd opt for the shower, and since cost is no barrier I'd make the whole bathroom into a completely accessible wet room

My reasoning:
there may come a point where she needs a wheelchair
she will likely need assistance doing the actual washing, and soaping up and rinsing off someone will be easier in a shower than reaching down into a tub, especially one of the high walled walk in tubs
once urinary and fecal incontinence become a problem it will be more hygienic to rinse off in a shower that to sit in a bath

Since you are renovating I'd also plan for a bidet sprayer or bidet toilet seat as well to help with toileting