If it is deep cut, you should have a vet look at it. Also, you need to watch carefully for signs of infection.
This has happened to many people...I did it years ago to one of mine. The best way to deal with mats is to put a comb under them (between the mat and the skin) before cutting. You can also put powder on them before brushing...that will sometimes help.
Stop beating yourself! Not like you meant to hurt her.
