You have to remember that girls have sexual urges too. Sometimes we want sex just as much as you do.
So maybe she's not being weird about it because it's a lie, maybe she's telling it to you in a weird way because she does physically want sex, but really does want to wait. That's perfectly normal and actually very likely.
Or Lance could be right. Maybe she's avoiding the issue and putting off sex because she really just doesn't want to do it right now; with you or not.
Whatever the reason, if she says she wants to wait, there's nothing you can do but wait. Don't push, don't prod, just wait it out or find someone else (which would make you a jerk, actually), and wait until she tells you she's ready.
Good luck,
~Sin