[X] Remain silent, thank her sincerely for her trust.
It doesn't matter whether or not Cai already knows. Ling Qi is not, to me, idealistic enough to confess. Cai already knew a bajillion factoids about Ling Qi, already got the scoop on her from Meizhen, and now that Cai gave Ling Qi something in return for that these two are even. Cai isn't a friend like Meizhen yet, where the score doesn't need to be kept.
Like, the update explicitly says that she and her thoughts are designed for the purpose of eliminating corruption in a way that Shenhua can't understand. Ling Qi is the corruption, and isn't a martyr willing to die for a cause. Ling Qi didn't run away from home because she had a moral objection to child prostitution, she ran away from home because she didn't want to be a child prostitute. And that's only been reinforced since arriving in the Sect. She wants a home, which is a very personal goal. It can and needs to extend outwards, yes, but she doesn't jive with Cai's topdown strategy game at all except as an individual unit. Ling Qi's drives and goals are about herself, not others, and there's nothing about that that needs fixing.