Hello LynnB
I wonder if your Mum has been put onto any drugs that she wasn't previously taking?
My Mum was put on a very low dose of Anti Psychotics and shortly afterwards started to refuse food and drink. The care home staff, the GP and the CPN all put the not eating down to the dementia but, cutting a long story short, we eventually stopped the drug and within 2 days she started eating like a horse and drinking well.
We have since tried another Anti Psychotic to try to control agitated/aggressive behaviour with the same results.
If your Mum is on these drugs it may be worth leaving them off for a trial period.
Take care.