Welcome BookRead66. I can give you my thoughts but you know that no one is a doctor here! Your daughter needs to see her doctor and have some lab tests to see what's going on. Here is a link to the Mayo Clinic about
Acanthosis Nigricans:
www.mayoclinic.org/diseases-conditions/acanthosis-nigricans/basics/definition/con-20025600. As you see, there is an association to obesity and diabetes.
Can you write what she eats for breakfast, lunch and dinner? When was the last time she saw her pediatrician? Besides the medical side of this matter, there's also her socialization, school, etc., so I think you need to consider the whole picture.
Do you have any family members who have diabetes? Please read the two stickies at the top of our Diabetes Forum for more general information. I'm glad you posted!