Hi there ... my big (little) sis has dementia too ... she's 79 ... fit as a butcher's dog but the dementia is going quickly now after 3 years relatively stable ... l can't imagine how your feeling now with a cancer diagnosis...  but I do know we'd not put her through chemo if it ever comes up ...

The only good thing is the dementia will mean she doesn't remember the cancer ... if you or her want treatment, you have to go down this path with your wishes ... together ... 

Always here if you want someone who understands what dementia entails ... so whatever you decide, my thoughts are with you .... take care ... Chrissie xx