Sometimes we try to make more of a situation than it is. She says she pulled the knots out because she didn't want to have to brush the knots out of her hair. She's sad. When we are mourning we are more sensitive to things such as brushing knots out of our hair. She found a way to not have to do that. We know that her idea won't help. So we problem solve with her about how to keep the knots out of her hair. Karma and Ava have excellent ideas.
If you want to cut her hair, include her in the decision so that it doesn't feel like punishment. I wonder why she would think it is punishment. Have you threatened to cut her hair if she didn't take care of it or for some other action viewed by you as misbehavior"
She may not be able to adequately take care of her hair at 4. My granddaughter who has long, very curly hair gradually started takinging care of it at that age. At 8 she is finally able to manage her hair most of the time. One consession that her mother has made is that she doesn't have to get all the tangles out. Her hair is full enough that some tangles are not noticed. If her hair looks a mess she pulls it back with an elastic band and she set to go. Hair just isn't worth fighting over.
Find a way to keep the tangles to a minimum with use of products and a good comb and brush. My daughter found tht a brush with plastic coated wires spaced a ways apart worked best. The base was squishy. The combination of wires and give of the brush made brushing thick hair less painful.
It is reasonable to say, not in anger, but as a necessary way to make life easier, that if mommy can't brush out your tangles we'll have to get a hair cut so there won't be so many tangles. However, my granddaughter wanted her hair cut to just below ear level so it would be like mama's. It still tangled (less so) and didn't look anything like mamas. She grew it long again.