Does your American Girl dolls hair resemble the hot mess express? If so I have a great tip for you it is called the Hot Water Dunk!
Key elements to the hot water dunk:
1. Protect your doll. Cover her with a plastic bag and make sure to cover the eyes.
2. Take the water just to the boiling point no need to go further.
3. Go slow go slow go slow!
I have not hot water dunked a curly haired doll but my understanding is that it will straighten it unless your dolls hair is in rollers. Keep this in mind.
When I have dunked a doll I did the following things. I brought the water just to the boiling point. While the water is getting there I prep my doll. I put a plastic bag over her body and cover her eyes with painters tape. When the water is ready I slowly and carefully dunk the dolls hair into the hot water and make sure to go to the edge of the hairline but not beyond. Once finished with this step I let it cool for just a minute and squeeze the excess water out of the hair. I then carefully brush the hair and lay the doll on the edge of a table with her head hanging off to dry. It will take a few hours for your dolls hair to dry completely. Once dry she can be unbagged and untaped. You want to wait for the hair to dry so you do not leave water marks on her body.
This can make your dolls hair look so much better. Remember to go slow and take your time. Some dolls are beyond help and will need to have a new wig. Pictured is a Kailey doll that was dunked. Not perfect but a good improvement.