Problem: The hair was dirty and was cutted to different lenghts.
If you hate rerooting, you can decide to cut her hair. Example for 80s layered style.
If it no succeed, then you should rerooting, but at least you practiced hair cutting of dolls.
But why not? There is nothing to lose.

1. Wash and detangle the hair
2. Cut the hair in layered style
3. Style it with hair curler on 80 Celsius