Sure, no one's a mind reader, but determining whether a girl is into your invitation usually isn't a great mystery. If she hesitates noticeably or tells you she's too busy to hang out, you can probably consider it a no—and pushing the point or trying to make her commit to a plan will only make her uncomfortable. At this point, you've made your intentions clear. Maybe she'll reach back out when she's not busy, but if she doesn't, move along with confidence. You deserve someone who is ready to make time for you, and a forced date is no fun at all.