Hi and welcome to YT
! Congrats on the new addition to your family...but I'm sorry that it was under sad circumstances. Bless your heart for keeping this little one in the family though, that's just so wonderful of you. To answer your questions:
1. She's always been fed wafer thin chicken, is this dangerous and is there a similar alternative?
Do you mean she is fed chicken, and nothing else? If yes, then the diet is probably unbalanced a bit. You may want to feed canned, raw, or kibble...but still add in her chicken that she is used to...would that be doable?
2. She snores a lot and makes piggy noises is this normal?
Snoring is not too unusual, but it can indicate something a bit structurally wrong in the throat area....meaning, other issues could occur as a result too, such as GERD or similar. You don't suspect GERD/reflux or anything do you...?
3. How long does she need walking and how many times?
She'd probably do just great w/ 1 or 2 walks a day...1 would probably be just fine.
4. We have a cat , how can we help them to get along?
They may just take some time to adjust naturally to each other. You could also take 2 small scarves/cloths and rub the scarves on their respective bodies, then have the cat wear the scarf w/ the dog's smells and have the dog wear the scarf w/ the cat's smells.
5. As my mum was ill for many years with no garden access she relied on puppy training pads , can I re toilet train her or is she too old?
This could be a tough one do, a real tough one...but certainly not impossible if you're really determined. I'd recommend you read the potty training stickies in our General Training section.