Parents and caretakers: How do you get a preschooler to be willing to let her hair be brushed?

I have a 4 year old daughter with long hair. She does not like to let me brush it. She says it hurts. Her hair is not particularly knotty and I try to be gentle, but it’s always a battle and she squeals and says I’m hurting her. I try to hold the hair and brush the ends so it’s not pulling her scalp, but still, she usually does not want it done. She has never had it cut (or let me cut it) because she says she wants it long like a princess.

I don’t want to threaten her and say if she does not let me brush it I will have to have it cut, but that’s the reality (not that I would cut it short, but it would need to be trimmed if she’s not going to let it be brushed). I don’t like to have her with her hair looking like a scraggly mess, but I don’t know how to convince her to let me brush it. Sometimes she’s willing but more often she is not.

Any advice for getting the preschool aged child to be willing to let me brush her hair?