old girl peeing her brains out, help!

hi
i am catsitting my sisters cat. Mickie is 16 yrs old and looks well except for one thing- she drinks and pees more than my diabetic old boy cat!!
i tested Mickie and she does NOT have diabetes
she had a senior blood panel done less than 6 mos ago and it was fine

my sister and i are concerned about a potassium deficiency as she does have a little muscle weakness

anyone have a cat on potassium supplements?
is there any way to get the right dose without blood work?
like, could you use urine instead?

this cat is EXTREMELY upset by blood work and just going out at all stresses her out
we don't want to put her thru anything we don't have to!!

any ideas greatly appreciated!

Get her to a vet- quickly! regardless of whether or not it will upset her, she needs blood work and a vet to determine what is wrong. With her age it could be anything. I am sure your sister will understand considering the situation.