Hit her up like once a week. No less. longer is cool too, but test it out. I've had chicks like her who I've only hit up like once a month and they were cool with it. The less time you spend with her, the more she'll value the time you're around and want to do whatever she can to make sure you come back. If you ever feel like shes getting an ego, then add another week. Every now and then hit her up just to talk for like 30 mins like you actually care about her life, or try to talk to her about stuff when you're chilling right before sex. I know you wont want to, but that will save you from the "all you care about is getting head from me" talk, and her feeling used and changing her mind. Chicks like her will give you money or whatever you ask for if you're nice to her