My 3yr old girl has gotten green discharge in her undies twice now. she does not complain of pain, burning, itching, or pain while urinating. could this be a vaginal infection at her age?

This is often due to a retained foreign material in the folds of the inner labia or the vagina itself. It can also represent retained soap from sitting in a soapy tub bath. When they cross their legs soap enters and may not be rinsed out effectively. I consider doing tub showers for a while, having them stand for soaping/rinsing with no sitting in suds. If it doesn't clear soon see her doc.

Most cases of vaginal discharge in young girls are caused by "nonspecific" vulvovaginitis, usually harmless. But yeast and other iinfections also are common and can be serious. She should see her pediatrician ASAP. Don't try to treat her with anything until the doc has evaluated the situation -- that might make diagnosis more difficult. Good luck.