senior cat, weight loss and clothing

My senior cat, Kyoko, has the beginnings of kidney failure, so is on the KD special diet, and is taking thyroid pills.

Despite being on the pills and the KD for about a year, she is still very underweght. She will eat if I am with her and hold the food for her, but otherwise she will cry for food, but not eat it.

Will I be doing any harm to her if I mix in regular canned food, like th science the diet, in with the kd once in a while, to try to get her eat more?

Also, I'm thinking of getting her a cat sweater since winter is coming on. Has anyone had luck getting an old cat to wear one?

Thanks!

Please read the CRF thread... it is the sticky at the top of this forum

Can a NON RX diet work ... YES BUT BUT YOU need to get her NUMBERS for blood work and work with the VET