Best food for thin cat with unknown health conditions

[Pootle22]

We're feeding a very thin cat, around 5 years old who has lost her front teeth. She appears to be improving.

Can anyone suggest the best food to try?

There is a huge back story to this but its irrelevant really. She has seen a vet (who removed the teeth) but the owner is doing no further investigations and will pts if she deteriorates further. Owner is happy for neighbours to try to feed the cat. Rspca are aware and do not feel the need to intervene.

Royal canin ageing/senior stage 2 - we were recommended by the vet when our cat lost some weight due to no apparent reason, he wasn't I'll. Basically, any easily digestible protein in big quantities- feed for the weight you want to achieve.

Just had a look, definitely better than the stuff I'm feeding. I'll buy a small bag and see if she'll eat it, thank you.

Ive been googling kitten food, wondered whether that would be suitable? She is hungry but runs out of steam quite quickly and leaves. Usually visits me twice a day though and my friend sees her at lunch.

Does she have worms which are sapping her nutrition? Vet could advise.
It’s lovely that you are caring for her. I’ve done the same with feral cats in the past.