Well done on getting your mum showered, even if not every day its still a victory and sounds like you were quick thinking with silly games to lighten things up. I was going to suggest leaving light on in bathroom and door open on a night but then read previous replies. We used to do that when my niece and nephews were little and were staying over.
When mum stayed last year a few times we did it for her after she got confused first night and couldn't find landing light switch to put light on, so we left bathroom light on. It helped her find bathroom but she turned light off as she left bathroom though so if she needed loo again she couldn't see where to go next time
So then we got a battery operated light with a sensor on from b&m and put it on the landing, as soon as she came out of bedroom the light came on and she could see on landing and as she walked past bathroom with door open she could see where to go. The bathroom here is next to spare room so easy for her to find though so may not be as useful for you.
In the hospital on eldery care ward all the toilets had big labels on door with a picture of a toilet on and said toilet. You could print your own off and blu tak it on the bathroom door. It may not help though if she doesn't notice it or recognise sign though and I suppose not being able to see bathroom directly when she comes out of her room is probably main problem for your mum though, not sure what you can do about that.
The pressure mat we got for mum when she was going to stay here at christmas was quite loud, it had different volume settings but I think it would be loud enough to wake up anyone in same room as receiver unless a heavy sleeper.
Could you put a doggy stair gate across stairs on a night to stop dog sneaking up and allow easier access to toilet for mum or does she need to access stairs too?
@anxious annie 's glow in the dark arrows made me smile, they'd be good, or those lights that come on on the floors of planes to lead way to emergency exits.
Seriously though it's a hard thing to get round without you losing sleep and that's not fair or good for you so I hope you can find something that helps ?
Hope you get a bit of time to do something nice when Mary Poppins comes this weekend besides soffits ?