My 14 year old experienced a relatively small patch of alopecia for a period of time. Her pediatrician said it would grow back and thankfully it did (yes, they are very appearance conscious at this age). My non-medical opinion is that it is related to stress. And often times our children keep their stress to themselves and we don’t really know it is happening to our sweet young ones. If there is a way to find out if she is suffering from undiagnosed stress, I would suggest looking into it.