Ask for your mum to be assessed to see if she qualifies for Continuing Health Care. It's not easy to get, but at least ask for the initial checklist to be completed. If you search the forum for this or the abbreviation CHC you'll find a lot of discussion about this topic.
The NHS will only fund your mother's care if she gets CHC funding. Otherwise she will be self-funding unless her savings/assets are below the £23,000 threshold.