My mum doesn't shower every day and has the wash at the sink. What I have noticed is that when she showers or takes a bath she is absolutely exhausted and hardly has the energy to get dressed after.
My mum likes a bath so I will run it for her with bubble bath in. I also put out some clothes in the bathroom so she doesn't have to go through looking for something to wear. Sometimes she doesn't wear what I put out and puts something else on. But she is also exhausted so a nice cup of tea and she's out like a light sitting on the settee.
My mum likes getting her nails done so she is quite happy. I don't remember the last time she did any laundry and she doesn't put anything in the basket as she has only worn it once! When I visit I gather up everything and do the laundry. I am sure some of it hasn't been worn at all but it's hard to tell so I just do the lot.
Perhaps it is just the simple task of showering or bathing that is getting too much to do daily for your mum. Perhaps you could coax her with the offer of some pampering like doing her hair, her nails or putting on the body lotion, a massage etc. This can also be very relaxing and calming. My mum likes the pampering a lot and these are some of the happy moments we get together which are the ones I hope to be able to look back on in the future.
There are the odd days when mum stays in her dressing gown. Provided it's not too regular and every day, I'm happy if she's happy. We have had rails put on the bath and
next to the shower for her to hold onto when she is there for reassurance. She needs them.
With dementia she will deteriorate over time and not manage the things she used to but just old age will be taking it's toll as well and perhaps she knows a shower or bath will tire her out. Her sense of smell won't be as good now and she wouldn't be aware if there was a slight odour. It hasn't reached that stage though.
If your mum isn't too energetic though she won't be breaking into a sweat which will help.
Mum is very stubborn and takes exception to us doing lists of things. We need to so if my sister's or brother has been in we know what needs doing and what's outstanding. Mum doesn't follow the sequence and resents finding any accounts or anything as she feels she is losing her control. She often says she feels useless. I try to reassura her by telling her she deserves a bit of help after all she has done for us. I know this lack of control issue is a reason she doesn't take advice so I try not to give it because if something is fixed in her head it will only annoy her when given and then the advice will be instantly forgotten but she will remain unsettled and not knowing why.
I have heard from others that small changes such as a bath mat can make a huge difference to people wanting to get in and out. It might appear as a hole or something unsafe to them but they won't say. If you have one try taking it away when she goes into the bath/shower and put it back for her to get out and see what happens. If she has sight of a mirror whilst in the shower/bath try changing the position slightly. If you haven't got hand rails there try putting a couple in. Trial and error I'm afraid and just when you think you've cracked it, it all changes again.
Hope you find a solution.