what does "Beneath her mask of an instinctive thoroughbred she had always been on to herself"mean?
"Who is he?" I demanded.
"A man from Savannah."
"Are you in love with him?"
"Of course I am." We both smiled. "Of course I am! What are you trying to make me say?"
There were no doubts, as there had been with other men. She couldn't afford to let herself have doubts. I knew this because she had long ago stopped making any pretensions with me. This very naturalness, I realized, was because she didn't consider me as a suitor. Beneath her mask of an instinctive thoroughbred she had always been on to herself, and she couldn't believe that anyone not taken in to the point of uncritical worship could really love her. That was what she called being "sincere"; she felt most security with men like Canby and Earl Schoen, who were incapable of passing judgments on the ostensibly aristocratic heart.