Rose Young's lack of endowment in the chest area was a huge source of insecurity when she was younger. But now that she was a mature, grown woman, it was a source of motivation instead. It made her want to prove to everyone that she didn't need a large chest in order to become attractive to the opposite sex. She used her brains, independence, and success in her career to impress people, especially men.
In addition, her ex-lovers could all attest to her great skills in bed. Large breasts could only do so much. It was all about how she used her body and fed a man's ego. So what if she was flat? All of her previous lovers still continued contacting her to this day, wanting to fuck her again, even though she already broke up with them.