Animal Care Needed

My cats name is Boo. Shes a long-haired black feral rescue that I got 2 years ago. It took me 9 months to get her to let me touch her, and that was when the rest of the house left on vacation. She sits on my bed in my room, she lets me pet her and give her snacks. Ive never been able to pick her up. About 4 weeks ago we started noticing she has some mats starting on her butt. I can brush the rest of her lightly, but she leaves if I try to brush the mats.