Even a leaky boat has three pounds of nails, let alone an entire former kingdom.
Lu Ping'an's act of taking disciples is a political event; the quality of the disciple is not important, what matters more is whom he chooses... But given a choice, Lu Ping'an naturally prefers those with better talent and more pleasing to the eye.
At the very least, this "sensible" little girl was very pleasing to Lu Ping'an's eyes.
"...Come with me, I will give you a promising future."
The thing Lu Ping'an most appreciated was probably that the girl had no attachments or relatives, yet her character hadn't fallen into darkness or extremism.
Ability can be cultivated, but once character and morals are formed, they are very difficult to change.
She possessed the power to obtain everything but still exercised considerable restraint... Being committed to a mental institution might have been her predicament, but it was also a testament to her self-control and choice.
