My cat really hates being brushed?

So I have this 5 year old cat just for a few months now and we've tried brushing her and she just really hates it. I've tried brushing her really gently but she gets really agitated and just scratches it and growls at it, And I also have 2 combs and one that resembles a huge toothbrush but she just simply hates all of them. I'm surprised I can even clean her (we have the leave on shampoo so she doesn't have to take a full on bath as often).