You don't mention how old your cat is. But what you are describing sounds quite serious. You should go to your vet to check her, do the bloodwork and chest x-ray.
Could be primarily respiratory problem (infection, asthma) or more commonly cardia...

The age is quite decent and would deserve a little bloodwork.
Anorexia in cats is very dangerous since they get the Fatty liver disease and will die without expensive vet care.
Just do the bloodwork (cost around 100$) and that will screen a...

First make sure u switch gradually to the new diet (over 1 week.
Can use any good brand. Best are Royal canine, Eukanuba, Science diet.

Quickest way is to shave the chin comletely, wash it with betadine solution (iodopovidone) make sure it's well diluted (light tea color so you don't dry the skin too much and then apply Mupirocin ointment (can get in vet's office)which is an antibiot...

When having long-haired cat you can help her with grooming, if possible on daily basis. Get a comb in the pet store and brush her. It will reduce amount of hair swallowed as well improve a bond with your cat.
Laxatone is is a good idea as it was...

Try urinary diet from Royal canine. My cats are very picky but they love Royal canine which offers perscriptions diet as well as regular ones.
Good luck.