ahh yes great question. I happen to be quite experienced in this dept. If she lived in the UK with you I would tell you to contact her very seldomly. Like only when you want some a$$, lol. If you contact her too much, she's gonna think you want a relationship, and depending on what she wants, she's either gonna start liking you or she'll run away. Again, it depends on what she wants.
However, if you contact her less, like once during the week and once on the weekend, she'll be around and should chase you. Actually, it's probably better to only contact her on the weekends if all you want is a booty call. She'll get the picture.
But in your situation, your booty call is only visiting. And she's only gonna be here for a few more months. In this case it's ok to contact her more because you both know she's leaving soon. Your gonna wanna make the most out of it. It's basically a time constraint, therefore you wont scare her off no matter how much you contact her. Ok maybe if you call her everyday then maybe she'll get weirded out, so don't that. But you get the picture. You can bascially contact her a few times a week, and on the weekends. Of course this goes with assuming she's attracted to u and it sounds like she is.
Ok, my last point. Booty calls are great, but just be aware at one point she's gonna fight or flight. Meaning she's going to want a relationship, or she'll move on if it never progresses. It all depends on the chick and what she wants. I've had booty calls for years, and I've had booty calls for just a few weeks. Thats something you can't really control. Just rememember if you want a booty call, it's important to set the frame from the very beginning! meaning make it clear,through your actions (dont talk about it). that you want this to be pure physical. When you guys meet up always hook up and don't open up too much or give her an opportunity to open up. If you do she's gonna find a connection and want a relationship. Just be that bad boy who's great in the sack

By not pening up, your making yourself mysterious and making her wonder about you. Thats good by the way
Ok I'm done, good luck.