Bridezilla syndrome is running rampant these days, isn't it?
First, I hope your son is feeling better, the poor little guy, kidney infections are so uncomfortable.
Second, If it were me, I'd call her and cancel the consult, for good. You don't need the stress that this spoiled brat will dish out to you.
I had a similar situation a couple of years ago. My Dad had died unexpectedly overnight and I needed to obviously cancel a consult for that next morning that was scheduled for 11 a.m. I phoned the girl at 8 a.m. to explain to her that my Dad had died the night before and her response was not "I'm sorry" like any person with a heart would have responded with, but she said "so I can't come for my consult?"
Emotions got the best of me and I told her that I didn't think I'd be able to work with her on her cake at all. Looking back, I'm not sorry that I sent her on her way.
The great thing about being self-employed is we CAN choose who we do and don't want to work with, and it's very liberating to tell someone to "Go screw!"