I found myself in a very similar situation, 150 miles away from a 90-yr-old Mum and dealing with my own cancer. She had had a couple of strokes and was housebound, suddenly living on her own.

First thing to do is make your Mum accept that she will need some level of help sooner or later. She will be dealing with age and her illness, including any side effects from her treatment. Next thing to do will be get that help organised, if only at a very minimum level, because it is a lot easier to ramp it up as required than it is to set up in the first place. Acceptance first, then admin.

Elderly care in the home varies wildly in cost and quality. Best quality and value for money will be from your Mum's local council - they will have a social care department. Typically they will assess your Mum's needs and recommend a care package to meet those needs. In my Mum's case, a carer popped round for 30 minutes at a time for breakfast, lunch and tea-time to make the meals, do the washing up, make sure Mum had taken her meds, and check on her overall condition. There was also a weekly dust or vacuum around the house to keep it clean and safe, and a service to get Mum to her hospital appointments and home again. Oh, and if any gadgets are needed around the house (perching stools, toilet frame, fall alarm, etc) the council will provide them too. Way better than trying to go private.

Care from the council is means tested, so your Mum may or may not have to pay. If she does, then her state pension should include an attendance allowance which will go a long way to offsetting that cost. And if, like me, you're a tad phobic with form-filling no worries, the social care dept should even help with that too.

Hope this helps, and good luck.
Steve