My Granddaughter Is 11 Years Old And Is Overweight.....she Has

My granddaughter is 11 years old and is overweight.....she has this dark ring around her neck that appears to be dirty......but it does not wash off. I have been told this is a sign of early diabetes. Her grandfather on her mothers side and mother of her father both are diabetic.....I have brought this to the attention of both parents and yet they have not had her tested....do you think she is in early stages of diabetes???? Thank you for any info you may be able to provide....