hi and welcome...can all be associated with allergies or intolerance within the diet., from the swollen mouth/itching to the diarrhea &/or Inflammatory bowel Disease (IBD)....but this may take some time to all sort out,first of all I will send you some links to do some reading and we'll take it from there ok.. there have been some problems with purina foods, you can check these posts out to see if there maybe a correlation there. how long has she been off this food?
http://www.medhelp.org/posts/Cats/consumer-reports-on-PURINA-Cat-and-Dog-food/show/1701333?personal_page_id=861539
are you feeding her from plastic bowls? these harbour bacteria, if you are change to ceramic or metal.
Do NOT feed dry foods, they are full of preservatives and tons of other additives.
I'm not real familiar with Tiki foods....I think they have a fairly good reputation, however for cats with any allergies or intolerances the diet must be GRAIN FREE...grains are a common allergen.
If you are feeding chicken as the protein...change it to a novel protein such as beef, fish or venison...venison is a very good choice however in my experience most cats don't like it...but well worth a try.
remember if you are changing brands to do so slowly or this will cause even more GI upset.
I will send you another site, this one is all on foods and why not to feed dry..how it can cause IBD. this Vet also has great info on how to transition to a wet diet, she also list the best grain free commercial diets...just click on the right side of her article for this info.
www.catinfo.org
this site I will send you to look at the photo of 'indolent ulcer' see if you think it resembles your kitties lip....good article all abt EGC and allergies there too....just whatever you do DON'T resort to the steroids or cyclosporine that it recommends...they cause many more issues, I think knowledge and some other changes are going to work without resorting to that drastic a medication...
http://www.marvistavet.com/html/body_eosinophilic_granuloma.html
also on the bottom of that page click on where is says...'more information about food allergies' again more good info.
well there I've given you tons to read for starters...come back after a read and we'll take it from there.....don't give up hope for dear Butterbeanā„