If your question is how do you greet a person you have never met before in the street, you can just say 'Hello', 'Hi', 'Good morning', 'Good afternoon', etc. You don't need to use a title like 'lady', 'girl', 'Mrs', etc. in this situation.
You say "(about sixteen years old or twenty-six)" - are you really asking if we use 'lady' or 'girl' for women of different ages?