They have the right to "向對方通告楊丹離開時的真實情況".
楊丹 should be honest and responsible. But if she chooses not to, her previous employer has the right to let other people know.
If it is true that 1. she is not a 業餘選手 but try to be one, and 2. she 不辭而別 from her current employer. Then she does not have good credit, and her future employer should at least know about it. Why should her previous employer do her a favor and cover it up?