I am sorry to hear of liah's problems. Is she on any meds right now? has she tried any meds to help with her problems? and how is her blood work?
There are several things that may help... There are certain anti-inflammatories that can help with arthritis and may also have a slight beneficial effect against bladder tumors (such as deramaxx or priroxicam). You would need to ask your vet about these. However these should only be used if you know that their kidneys and liver are working OK.
Is she on glucosamine too? this is a good supplement that is safe and easy to use. however its effects may not be apparent for several weeks.
If she is having trouble eating she may be having pain trying to lower her heard to eat, so try handfeeding her raising her food and water bowls. I often suggest chicken baby food as a good food too to entice eating, its very palatable and they seem to like it. You could also try some cooked chicken or turkey.
If she is starting to have more and more bad days than good days despite medications to try and help and especially if she doesn't start eating again then you may have to start thinking about euthanasia, but you will know when the time is right.
Good luck