So sorry about the matting problem. :( Basically it happens because she probably doesn't groom herself as thoroughly as she used to. the cat's tongue actually combes the hair.
anyway, let me comment on some of the suggestions.
cornstarch will probably not help wth mats. I am sure it was used to help absorb some of the dirt and grease in the coat. But, it can't hurt to try.
Spray on detanglers might not be safe for cats. READ labels!! And you do still have to COMB the hair, so she still might resist.
The comb pictured above is a fantastic comb, I could not live without it, but it WILL still pull at the fur.
Shaving is the quickest way to get the offensive hair away, and the results last longer than just combing. But I understand not wanting sedation.
Call any and all groomers in your area and ask if they do cats. Your vet is not always the best option. We (at our shop) would be able to do what is needed without sedation. All you need is a shop with experience, a few exta hands, and the willingness to work within the customer's request.
Ask them to just shave the hindquarters. Explain that she is old and doesn't tolerate a lot of grooming, but needs this done for sanitary reasons. She should be in and out quickly before she gets agitated.
Good luck!
