Jun Wu Xie only revealed to the Twelve Palaces with three clues.
One, the use of Spirit Reinforcement was exclusive only to the Spirit Mastery Race.
Two, the Spirit Reinforcement race stood aloof from worldly affairs, and were hard to locate.
Three, she was not on good terms with others of her race.
These three points were enough to make the Twelve Palaces understand that before them, Jun Wu Xie was the only person that was able to use Spirit Reinforcement. Before the Twelve Palaces found others from the Spirit Mastery race, they could only depend on her to acquire the strength of Spirit Reinforcement.
And all these three points, were complete lies that Jun Wu Xie had made up.
To achieve her objective of making the Twelve Palaces unwilling to harm her in fear of losing that power completely.