^It sounds to me like they already offered the filly to the previous owners and they said no?
Bottom line is that it's your horse. If the filly isn't up to what you're wanting to do, there's nothing wrong with selling it, and I'm sure your friends will understand.
Bottom line is that it's your horse. If the filly isn't up to what you're wanting to do, there's nothing wrong with selling it, and I'm sure your friends will understand.