I'm sure the ladies with far more hair care experience will chime in with how to handle the damaged hair.
The only thing that I can recommend it showing your daughter in the next week how to take care of her own hair and also making sure that she is comfortable telling the adults around her what to do for her hair. She is only 8 years old and probably reluctant to say no to an adult, but in this instance you can give her permission to tell adults no when it comes to messing up her hair. And also show her what products you want used (or have them delivered to the house).
I am so sorry that this happened to your daughter
My friend had this happen to her too - and she is a stylist. Her mother-in-law permed her daughter's hair one weekend without permission.
Her baby will be 8 years old in June.