Should I let my daughter go to...?

My daughter was invited to a carnival by one of her best school friends. I think that there is enough social time at school and she doesn't need to hang out with friends on the weekends. The carnival is on a Sunday which is our family day and it's at a church. We are a very Jewish family. I don't really feel comfortable going but this is the first invitation she has got from a friend in a while because I usually say no. Also she will be eating non organically and that doesn't settle right with her tummy. Plus she will be introduced to sweets for the first time (instead of ice cream we have tart frozen yogurt, frozen gs instead of popsicles) and I don't want her to be exposed. Should I let her go, I have more reason not too, but I feel so bad she's so excited because for the first time I said maybe instead of no.