I often need a "hiatus" from friends, especially if the relationship starts to feel too intense. I think "needing space"--physical and emotional--is normal for most people. It allows us to maintain our separate sense of identity and priorities.
That said, when I was younger and friends needed space from me, I found it very difficult to give them that space. I felt they must surely be angry with me, and that I must have said or done something terribly wrong. Even when I had done something wrong, I could not understand that they would continue to like me if I just left them alone for a while. I could be very annoying. It's a good way to lose friends, bothering them when they need their space (and a guaranteed way to lose a date!).
Best I can suggest is, to set some goals for yourself which you can achieve in her absence. Some goals might involve, say, meeting up with other friends a few times a week, or doing some things you enjoy but haven't had time for lately. That way, when she does want to meet up again and you are both sharing the things you've been up to, she'll be thinking what an interesting person you are and how much she enjoys talking with you, rather than how needy and mopey you've been 