Yandevere was born with the second ranked corrosive flame, right beneath Devil's Wisp. Her flames were the Devil's Fog flames and were ranked 36th. To have a top 50 unique flame in her grasp, her future should have been practically limitless.
The truth of the matter was that Dyon didn't start truly questioning her intentions until the matters of the Demonic Gorge took place. Back then, Dyon had sensed the power of the corrosive flames hidden within the Devil Qi Vein, and clearly, so had Yandevere.
This was the first time Yandevere let some of her true disposition shine through. Dyon knew that she thought of killing him back then all in order to raise the strength of her unique flames.
However, this reality only made Dyon more confused. Yandevere clearly wanted to grow stronger, yet she agreed to breakthrough before she reached her peak strength. Now, she was forever relegated to the 6th Order. There was no changing this unless she abolished her cultivation.