It's somewhat clear... It's said that Bai girl was someone who Yang lord found with ordinary background but have many knowledge about cultivating and then he begin to love her.. Ordinary background ?? BULLSHIT :v
Bai could have been from a different heavenly world and could have been planted as a spy with mission to make sure that the yang heavenly world doesn't progress too much she had already memorized the 2 sacred manuals so she doesn't need to take it,only the sword tip would have been troublesome and thus she took it away with her,also the ruined meridian part made it so that the humans lose to the demons the divine lord seal.
Because she had consulted with the stargazer and know that in the near future he will have affair with the great Empress!! That sword is just the warning. Next time, it'll be aimed at that meat! Dont argue! Wife knows everthing!
Here's the likely scenarios: Jealous of his reputation. Despises his pompous attitude. In league with the Demons. In league with some secret organization which needed the sword tip. I'm betting on the last one. If she wanted resources, power, etc. then she only had to ask. She married the guy for those, obviously. She stuck with him for countless years, so why did she wait until he had returned to do what she did? By the end of the current chapter's description it hints that she had studied all those three treasures from the Secret Realm many times before. However, there wasn't much time since he returned until he won the mark. Then, he faced countless challenges over years until this one. All the while, she had time to study and research them. This just happened to be a convenient scheme to run off and break ties with him. I wouldn't be surprised if she was tied to the Blood Moon.
She was a sex slave of that demon rival, who ordered her obedient ass to shake it until she finds the opportunity to strike the yang emperor down before their duel.
It's impossible to know unless we reach that point since the TMW Translation already caught up with the Author
Morale of this chapter "Don't trust your weifu, especially after showing your winning lotto broken tip"