Old kitty who will not take medications... Do not know what to do :(

I have a cat named Chloe. She is 18 and feisty. Chloe has always been a one person cat, but even then she has struggled with her behavior with me through the years (biting, scratching, etc). She has become much more tolerant over the years, but one thing she will not compromise on is medication. Liquid meds end up everywhere except her mouth and I end up bleeding usually. Don't even get me started on pills or crushing them on food.
Over the last few years, Chloe has developed diarrhea and vomiting. She has gone from leaking odd clear fluids to leaking straight out liquid poop. She does not even know it happened until she wakes up in a puddle on the couch. The doctor has said its either cancer or irritable bowel disease. Her diet is not alter able, although it is already gluten free. We tried the injectable steroids to stabilize but they have not worked. The doctor says we can try oral tablets, but as I mentioned earlier he does not know what that really means in Chloe's world. I am struggling with the decision... Is it time for me to let her go? I have had her my whole life practically. I don't want her to suffer or be in pain but it is hard to know sometimes if she is. Thanks for the input.

Compounding pharmacies can change some medicines into a topical cream that you can rub on the cat's ear. Do you think she might tolerate that? Some cats can stand an injection better than a pill. but sounds like you already tried that. what about a different steroid? Did you try the budesonide? I don't know the background so I don't know or understand why you said her diet is unalterable, but I just thought I should mention that my cat with IBD -- who I could not easily put on steroids because he was already diabetic -- was helped a great deal by a venison diet, I fed about 2/3 raw and 1/3 canned, both Nature's Variety Instinct which was recommended by an internal med vet. See , he was not just reacting to gluten but to some kinds of meat protein. I know this because when he got into another cats food he was having bloody vomit and liquid poop. but when he stayed on the venison he was OK. Oh I also gave him injections of Vitamin B12. and probiotics. I basically got my cat used to a lot of medical things out of sheer bribery. he was extremely fond of some dried salmon treats and I used that to get him to accept things like shots and blood glucose testing. I admit that there was bloodshed ( mine) when I first tried though, and I had to back up and go through small steps of desensitization. I just don't know what all is possible for your cat, so I dont know what to tell you. If she is suffering more than enjoying life, and you have no way to control it, then it is time to let her go.

Comounding pharmacies can also compound medication into liquid FLAVORED formulas that you can mix with food.

The rule of thumb is:  if the drug is also used in humans (flagyl, prozac), then the pharmacist can compound the medication.  If the drug is not used by humans, the pharmacist, with the vet's approval, compound the medication.  ("rule of thumb" = what your state laws are).  I can't pill Ritz, forget pill pockets or putting butter then cream cheese insert in hot dog and then pill pocket:  she ate everything but the pill.  I was able to get Ritz to take flagly and regelan using a flavored (tuna & chicken) liquid.

Sometimes the vet won't give his approval if the medication is time(?) released, I guess designed to be dissolved slowly into the cat's system.  (Not technically versed in that type of stuff).

And I agree with maewkaew:  look to the food issues and regarding life:  quality over quantity.  Sad.  Vibes.

You may want to try the Greenies Pill Pockets though, my 12 year old was impossible to pill also, but ate all his medication in these. When he needs a antibiotic now, I take him in and get the injection that lasts a week, trying to pill him was just too stressful. You may want to start Chloe out with JUST the pill pocket until she decides they are a treat. You can crush the pills between two spoons and hide it in something she really likes also. 

Why is her diet not alterable?  I'm not sure you are really asking how to pill her, I think you are more asking if you should let her go or not, at least that's the way I am reading your post .  If she has IBD, then she is not comfortable, and probably in some distress, which could probably be prevented with a change in diet.  But then again, if it's cancer, than another story.  Can your Vet not determine if it's cancer, perhaps with a blood test (wouldn't her WBC be high?) 

What is her quality of life at this point?  Is she happy, eating, playing that sort of thing?  You know your furbaby.  What is she telling you?