When Amber was born, she surprised the doctors quite a bit; she looked entirely male, no vagina to indicate that's she was female, and adding to the confusion was the horse penis and testicles. Yes, even the sheath, Greg, of course, figure does that his 'son' was simply given a warped penis that surgery could fix later in life. But when the doctors did a test on Amber, and found out she was female, he just didn't know what to do.
Greg and his wife loved Amber, but a sister you can imagine, being an otherwise perfect girl with something that belonged on a horse (a Clydesdale to be precise), certainly did affect her mentally.
But, just how was his daughter affected, how did she treat her third leg?
->She's a nervous wreck trying to hide it
->She neither flaunts it, nor hides it
->Amber treats it oddly, nobody cares when they see a horses penis, so why should she hide hers? When it's erect, she just hikes her dress up over it and lets it out in the open. She's even banged a few horses because that's what a horse penis does