My daughter is 8, almost 9. She mainly just brushes her hair though but sometimes I’ll go back through it again after her. She just likes to leave it loose though but I guess this is around the age.
My daughter is about to be 10 and she does not do her own hair yet. But she is starting to be over me doing it. Her hair is big thick and curly too, so she still needs my help. She just asked me if she could get it straightened. I told her that won't be as easy to manage as she thinks and maybe when she's a little older. Point is, I don't think my daughter will be ready to manage her own hair for at least another year or 2.
My almost six-year-old likes to brush her hair but I have to go over it. She can put a headband in but that is it. I was about your daughter's age when I started wanting to do my hair. I did need help for a while getting it brushed. My hair was thick but not as long as your daughters.