Sorry to hear about Cleo, it sounds like you're doing everything you can. I just posted about my 16 1/2 year old cat & his health problems. I'm struggling for acceptance, too. Like you, I just love him to pieces and can't imagine my life without him, he's been with me for so long.
I hope your Cleo will continue to cooperate with taking her meds so she can be around for a long time. For years I had to give ChowChow a small pill daily. I bought a small morter & pestle and ground it up, & put the powder in a tasty bit of food (I usually used hamburger). It worked very well.