Been there... My daughter has a lot of hair. Came out looking like a Breck shampoo commercial! It was hard when she was an infant because she'd get food or spit up in it. You have to wash it every night. Get some natural conditioner from the health food store. People would say 'oh what beautiful hair she has!' but they didn't realize how much work it took to keep it from being matted and tangled.
Its not easy at this age. But you can't give up. Your daughter has to accept that brushing her hair is part of the daily get ready activities. Otherwise, you will be battling her on this when she 2 & 3... (5 or 6?!) and that's much harder battle to win. You have to see that all the effort you make towards brushing her hair now is training her for letting you brush it when she is older.
I did buy a brush from a beauty supply store that is made for use on extensions because the fingers are meant to bend instead of pull on the hair. That helped a little. But we still had to endure the yelling & crying phase... By the way, next up is the phase where she shakes her head wildly back and forth when you try to brush it...
I would also pick up portions of her hair and, holding that near her scalp, brush it to reduce the pulling pressure on her scalp, working gently on the knots.
(Oh, and brushing hair is nothing compared to trying to brush teeth!!!) Hang in there!