If the same thing went down a second time-- the employee had “appropriated” the item after having done that once before and was told that was wrong (either you had told her or I had), I’d come down hard.
I can’t have someone working for me that can’t follow directions or common sense (and also/or is stupid enough to wear the stolen vest to the scene of the crime. Actually, because that last bit happened, I think I’d be curious/incredulous to start by asking the employee WTF. In other words, if you told me that my employee had taken advantage of your accident and taken your vest, I’d want to hear her side of that. Anything other than an honest and plausible explanation would earn that “I can’t have anyone think stuff get stolen at this barn. Do you want to work here and can you comply with that? If not, no hard feelings, but there’s the door.”