I got my kicking strap fitted, had to install footmans loops to the shafts. Looks like it works and fits properlyI don't have any direct wreck experience to share, except to say that I'm sorry that happened and it sounds scary! But it also sounds like she was OK afterwards (mentally) so it was probably as your vet said something stung her. Sometimes when they start bucking for one reason, they kind of scare themselves and then buck more because they are freaked out and then if more things touch them that they don't expect while they are bucking, they might kind of panic.
The one thing I will say is that I added a kick strap to Rowan's harness after it became apparent that bucking was his go-to for just about any reason. His bucking has diminished considerably with further training but I'm leaving the strap in place. He's only tried bucking one time with it on and stopped as soon as he realized it wasn't getting him anywhere. It has also helped my confidence because I don't have to worry about getting kicked (I have a Hyperbike so he's RIGHT THERE) and so I feel more confident about sending him forward assertively which of course is the best remedy for bratty-type bucking. Andy Marcoux of Coachman's Delight has a blog post about properly selecting and fitting a kick strap so that it's actually functional, which I found helpful. I got one that has snaps on the ends so it only adds an extra couple of seconds to the hitching process.