Notes, emails etc are so easy to misread since you can't hear tone or see body language. I'd much rather talk to a parent in person than write to them but it's not possible to do that every day after school. We keep all our personal info private and only communicate via school telephone & a notebook we communicate to a few in every so often. I HATE writing in the NB
As a coach you have to have an opinion on matters relating to the team, like goodie bags, and hopefully you will be respected for this. If she replies and it seems like she's upset I would stop emailing her and try to talk in person. And also let your supervisor know, hopefully before he/she finds out from the booster!