Originally Posted by Saddlebag
Partial payment may not be an admission of guilt if you felt you were coerced/bullied into making payment,
The partial payment is not as important as the signed document. This is the OP's admission that her horse caused the damage and that she has accepted responsibility for it. Coercion is a valid issue, but she is going to have to prove that - which isn't necessarily easy. As I mentioned, it is definitely worth a shot if the OP really felt she was forced into signing (you don't want to lie in court).
since this is a man vs a woman.
I really hope that point alone is not enough to prove coercion. Unless the "man" involved actually implied threat of physical force (and was obviously able to carry through on such a threat) I hope gender isn't a factor for either side's argument. The other side of the sexist coin is that the BO underestimated the actual damages because the boarder wore a low cut top to distract him. :)