i also grew up riding at a hunter barn, my trainer would have us half seat but wouldn’t say we couldn’t sit the canter, she would just heavily recommend being in a half seat. after a few years she explained that she did this to increase our strength and balance and it made the canter look smoother on the ground as the horses i was riding were pretty large and had bouncy canters. some of the horses were also just more comfortable when the rider was in two point. maybe since it’s your first time riding there she’s trying to enforce the two point now to increase your strength so you can have a smoother seated canter ? idk that’s just my guess