What to say to this girl? details inside Please help I appreciate it?

I told this girl at my church that I liked her during camp and whenever i would say something she would smile really big and make it look like shes hypnotized by me. So she made me a bracelet and I made her one at the end, and now were back at church like normal, except she knows i like her, and she said at camp she wasnt ready for the commitment. But now shes smileying even more when i talk to her, but also when i say something dumb or wierd she will kind of put that face on like she doesnt want to hear it again, or she is not interested, or she kinda shy's away. Now. I just got the permission to ask her to go bowling with my sister,me, and my sis's boyfriend (21 years old) just to hang out since we cant drive yet (15 years old). But I want to find the right time, and I want to make sure she wont be creaped out if i ask her or anything like that. so how do I know if she will say yes or if she has any intrest in me? Since she always makes those different faces from time to time, (mostly the BIG shy smile ( shes blushing ) ). Thanks in advance. I appreciate the help.