Medicine that makes an elder cat sleepy is…not noticeable. 
Glad to hear she’s doing better. Sorry about the pricetag - when we took our elder cat in to get her arthritis looked after, it ended up being a nice, round $700 (vet check-up, x-rays, bloodwork, shot of something, nails trimmed, prescriptions - the whole she-bang).
Crush the tablets into a powder, mix with a small blob of butter and smear it on her foreleg, she will lick it off.
I noticed this weekend that my cat Nick was going from litter box to litter box without much scratching, so I took him to the vet Monday. He has a kidney infection (and I was told that he’s a fatty catty and needs to lose weight. 13.1 lbs isn’t fat! He’s just big-boned.
He gets banana-flavoured clavamox twice a day. Fortunately he doesn’t hold a grudge.
StG