Maybe the Revolution is bothering her. I would stop using it on her and see if that helps.
If you use any carpet freshener spray or powder on the rugs, stop.
It could be a problem with the cat litter. What litter are you using?
She might be allergic to an ingredient in the food you are feeding her. Animals, including humans, develop allergies over time. The most common foods cats are allergic to are beef, lamb, seafood, corn, soy, dairy products and wheat gluten. You need to do trial and error to pinpoint the offending ingredient.
My cat Earl is allergic to soy.
An easy thing to try first is eliminating corn, wheat, soy, fish, beef and lamb. Make sure with the canned food there is no wheat gluten. The types with gravy have wheat gluten, so just serve pate style- no fish or beef. Read the labels carefully. Get a grain free, chicken flavor dry food from a pet store. I use Before Grain chicken for Earl. Read labels carefully as some dry foods use fish oils in them.
You need to give it a good three weeks.
Information on food allergies in cats:
http://www.peteducation.com/article.cfm?c=1+1332&aid=142The vet likely will want to give Gelsey a steroid shot. That is what the vet gave Earl, and it did stop his allergic reaction, but threw him into diabetes!

( He recovered from diabetes after being on insulin and a very low carb, all canned diet.) After he recovered from diabetes, I started him on a little dry food to see how it went. It was fine blood sugar-wise, but the dry food I tried with him was Purina One. After a while, his allergic symptoms came back. For sure I was not going to let him have another steriod shot, so I did trial and error with foods to check if there was a food ingredient causing the problem. It turned out to be soy.
So, do take Gelsey to the vet, but if the vet wants to give her a steroid shot, ask if there is something else to try first. Maybe an antihistamine.
Cats seem to tolerate steroids well, but not all, such as Earl.