Buying kids' shoes without trying on is not easy (and actually not recommended). But sometimes, you might want to buy shoes as a gift. And bringing a pair of shoes (that may fit) is a lot more fun than bringing a gift card from the shoe store. (But make sure the shoe store has a fair return policy!)
The chart below will help you pick out a pair of shoes based on girl's age.
But always remember that kids' feet are different - our Shoe Size by Age Chart is just a guideline! Good luck!