Old kitty is slowing down

My cat is 13 years old female long hair calico. We got her as a kitten from a family farm. She’s lived indoors ever since we good food and visits the vet. We take her in monthly for shots for arthritis in her hips. She goes in on Tuesday but I can tell my old girl is hurting. She’s not greating me at the door. She sometimes will come and cuddle if I’m on the couch or in bed. She’s got a comfy spot but lately won’t even raise her head to look at us. She’s been eating some but never has been food driven I almost never see her eat since I’ve had her. How long do I drag her along I can tell quality is going down hill for her. But she’s the sweetest girl. Vet can do anything to her. Anyone can pet her or hold her. She’s the greatest kitty there is. But my old girl is hurting.. what should I do?