Mum 91 stage 4 lung cancer (spread to liver)

Just venting really. Mum has recently been assessed as likely having dementia and referred to community mental health team but this has been superseded with the cancer diagnosis last week. I’m now unclear if she has dementia or if the cancer has spread to the brain as the McMillan nurse explained that’s what will (if it hasn’t already) happen and the presenting symptoms will be the same. So that’s one aspect of it. I suppose in some ways it doesn’t matter which it is - the symptoms are the same. But it’s tough. 
The second issue is she lives alone and she is fiercely independent, to a fault. She won’t have a carer but things are deteriorating.  When I went round yesterday, she hadn’t  taken any meds since Tuesday morning and the house was freezing. I worked out the boiler was off. She’d rang British Gas (a plus!) who were going out today. Except all it needed was the pressure topping up and I fixed it in 30 seconds. So she would rather have been freezing all night instead of ringing me for help. 
I just don’t know what to do. Social services say she doesn’t hit the threshold for care and she’s refusing privately funded. I can’t be there 24/7 (I should add I am an only child with absolutely no family for support, work full time and am an older mum to a 14 year old). 
I’m exhausted already and it’s only going to get worse. 
any tips to a) manage her and b) manage me (!) would be amazing!