The BO probably should have checked that her worker did the job correct.
I would be upset if it had happened to my horse, really upset, and I am Not Nice when it comes to my animals health.
I would have said something right then and there, had my horse at the Vets and then moved from the Vets to another facility.
Since you stayed, had the BO help with after care it changes your position. as I stated in a prior post you would owe her for the additional car etc. To sue now would be spiteful. IF you insist she pay, go speak to her first. Be prepared to move your horse.