Hi J.,
I'm sort of going against what everyone else is saying here...but I think any sort of toy / gift will be fine. My family is very Catholic, but usually, the "religious" gifts are left up to the God parents and any other "older" members of the family. Unless there are very few people invited to the First Communion party, the risk of giving duplicates (of bibles, rosaries, etc.) runs high. Amongst my own family and friends, we just mostly give non-religious gifts, just something that a little girl (or boy) that age will love. Could be a toy, could be a book of some sort, could be anything that you might normally get for their birthday. If you're comfortable doing so, you can always ask the little girl's mom what she might like...but if you're not comfortable, just pick out something you personally like and give a gift receipt. I remember for my own first communion, my aunt and uncle gave me a Nerf soccer ball--that is the ONLY gift I remember 26 years later (aside from the prayer book from my Godmother) because it was my favorite thing! Hope this helps, good luck!