Oh OP, what a difficult situation for you.
You absolutely didn't make her hoard or fail to provide what she needed.
Hoarding disorder is classified as a mental health issue and is quite complex - I'm a professional organiser but do not deal with clients with hoarding disorder, purely because there are people better trained to do so. I would never want to do more harm than good.
Anyway, back to your mum's home. Self care is just as key as the clearing here. Try to get out of the house during the day between clearing sessions, for a coffee / trip to the off license / to watch the birds. Hydrate. If you need to take extra leave from work, do it.
If you can get additional help for the coming days, do. Focus first on getting the stuff that is clearly not valuable or useful (eg stacks of newspaper, old food wrappers or containers) out of the house - a skip may we'll be needed. My grandma left stacks and stacks of needlecraft magazines. It would have been lovely to pass them on to someone who would've appreciated them, but in reality we had about two weeks to get her housing association flat totally cleared, so that wasn't a priority.
I second what previous posters said about selling - if you can enlist a third party to take charge of that for a selected 'chunk' of items, great. If not, consider how much time you have to dedicate to selling on fb etc.
In terms of items that aren't got rid of, try to think in terms of 'what do you want to keep?' instead of 'what do you want to give away?' - the subtle difference can have quite a big effect on the amount kept.
If you want to chat about anything specific feel free to drop me a PM.