Another way to do it is to go to the person's profile. On the left of the profile, there will be a link that says "Report/Block this Person." A box will then pop up that gives you the option to either block or report the individual. The block option says this:
"If you block someone, they will not be able to find you in a Facebook search, see your profile, or interact with you through Facebook channels (such as Wall posts, Poke, etc.). Any Facebook ties you currently have with a person you block will be broken (for example, friendship connections, Relationship Status, etc.). Note that blocking someone may not prevent all communications and interactions in third-party applications, and does not extend to elsewhere on the Internet."
Under "report" they have a drop down menu for reasons why you're reporting the person. "Unwanted contact" is one of them. So if she's really bothering you, that's an option as well.