Just be polite about it, and you'll be able to easily find out whether she is dating someone.Shared friends can be a wealth of information if you ask the right questions in the right way.
You can do that through checking out her social network accounts to know if the girl you like is already taken by looking at her social pages.
In fact, some cultures have very strict guidelines.
Of course, it also depends on circumstances like where you met her, how you know each other, and if you have common friends.
We discussed this in the main guide, particularly in the section on Facebook Stalking.
While social networking sites such as Facebook, Twitter, and My Space are great places to share your interests, background, recent activities, and real-life communication with your loved ones, they also let people see what you are doing.