The knocking girl

So I have this student, let's call her Student A. She is quite possibly the most rude girl I've met. Don't get me wrong, I like her. She is one of my "library kids". This refers to the kids that hang out in the library whenever possible. But she has this really bad habit. When she is ready for service, not that I am in the service industry, she knocks on the desk until I pay attention to her. So here I am, working at my desk. A lot of the time I am typing or obviously reading something and instead of waiting patiently at the desk for either me or my assistant to help her she starts knocking. And she doesn't stop. She keeps doing it until a) we look up and aknowledge her or b) get up to help her. I'm not quite sure why she is in such a hurry, but it never fails. She comes up at lunch and "knock, knock, knock". She comes up before school and "knock, knock, knock". I wonder if she has any idea how rude or annoying this is? Either way, my assistant and I are sure to NOT jump up and help her. In fact, we take our sweet time just to watch her squirm. Does she get the hint? Oh no. So until she figures it out OR I throw a book at her, she will be "the knocking girl".