What do I do about a girl who wants to wait until marriage to have ? (Seems crazy doesn't it?)?

Okay. I am in college right now and 19 and in the past semester or so I've had with maybe about 15 girls? More or less, I guess thats enough, some of my friends have had it with a lot more. Anyway, back from break I've met this today girl who doesn't want to have with me tonight. While all my other girls had it with me on the first day (normal) she wants to wait until marriage (reactionary and stupid). What do I do about this abnormal behavoir? Should I call a psychologist? She isn't Muslim either for she is white and is evangelical. This is so strange! Why won't she do it! I tried going into her dorm room but she locked the door! I feel so offended! Why won't she give in?