Like Hissy said, be VERY careful not to cut her skin. It can be very hard to determine where the skin stops and the mat begins, if you've never done it before. I would use a comb to get between the mat and skin, then cut. Or, take her to a groomer or the vet and they can shave it out. When my cats mat, which can happen quickly, I just use a wide toothed metal comb to pull the mats out, then rub the area to eliminate any discomfort. They don't seem to mind that, if the mat isn't too big.