I agree that she should know why it is important to wash and separate. I would occasionally check and separate (cause it can be difficult), but I would leave the washing up to her.
My biggest concern would be does she really hate them? Or was she just saying that in frustration? I know that she chose to dread her hair. But why did she choose it? Did she choose it because she really wants dreads or because of your love of dreads.
I took ballet lessons til i was 18. It was very important to me. I had great passion for it. When my daughters were young I signed them up. I thought they would love it as much as I did. They were very excited at first. At 3 years of age it is fun and games but as they get older, the classes became more serious. They had no love for it at all. They were taking these classes for me. They thought I would be hurt or upset with them if they wanted to quit. Children strive for our acceptance and approval. They don't want us to be disappointed in them.
So if she wants to dread because it is important to her, she will take care of them. If she is doing it for you, she may start to resent them. She may have wanted them in the beginning, but changed her mind. If she doesn't want them anymore, I would not talk her into it. Because then it becomes for you and not for her.
You are an incredible mother. Many parents won't allow their children to express themselves. You not only allow it but you encourage it! That is beautiful!!!