I totally agree with this. That would probably be the best response. She might not like it, that's true, but it is also true that she seems to have forgotten that you are grieving and affected by your Dad's traumatic death too, not just her.
You have both suffered a lot this year, and losing a parent and/or husband in a traumatic way like that is horrendous. I know. It happened to me four and a half years ago when my Dad died and he wasn't even at home (died in hospital alone of multi organ failure during covid lockdown, though he didn't actually have COVID).
Since my Dad died even my mother has always refrained from sleeping on his side of their bed and he didn't even die there. It's HIS space. When I visit I sleep in my own bed there , which is still in my childhood bedroom.
Your mum is still being unreasonable though and I think you do need to put your foot down about some important things here. I'd tell her that you simply cannot sleep in his deathbed as it would be too triggering. If she mocks or poo poos you for saying that then I would just not go at all to be honest. The carpet stain is also very triggering and I would also want that replaced too. To be honest, I'm rather surprised that it doesn't seem to bother her enough to have done something about it (like new carpet).
Of course this could ignite an argument, but if she does carry it that far then it is an argument that needs to be had, I'm afraid.
You matter too, just as much as she does. True that he was her husband, but he was also your Dad and that is not insignificant so don't let her act as though it is.
Personally, I think you need to tell her about your cancelled holiday. At the moment she probably can't see that you have compromised at all, so it might just give her the pause for thought that she needs.
Of course you don't want to leave her on her own this Christmas, but she needs to understand that although no-one wanted this, things have changed and that you can only help her if she takes into account that you are affected too and your feelings are also valid.