I agree, don't second guess yourself! If she really had a problem with it, she could have been more mature about how she handled it. Sounds like she is just one of those people who like to focus on the negative.
The tough part is explaining to your little one about why her friend can't come over

I myself, would go up to the Mom and ask her if you've done something to upset her ~ mentioning the snacks and let her know that snack time will be avoided if it is a problem as it shouldn't be something the kids should stop playing over. ....see what she says.

You have no need to explain yourself for what you give your kids and yes..it was a party!!!