My 13 year old girl has veins on her legs. Could they be varicose veins?

Without a picture, it can be hard to tell. However, your
daughter may indeed have unhealthy veins of some sort (though they may be
reticular veins rather than varicose veins). Is there a history of vein issues
in your family? If so, it may be prudent to visit a vein specialist, as
unhealthy veins can be hereditary.

Thank you for your question.She is likely to have reticular veins or small varicose veins and underlying venous insufficiency.Treatment is not necessary unless she develops symptoms or reaches the age of 16.Read my ebook about venous insufficiency on the link below. BestDr. Karamanoukian

From what you describe the veins sound like reticular and not varicose veins.  A picture would be helpful.  Most likely this is normal. You should see a vein specialist.