[X] Sincerity
[X] Mischief
[X] Spirits
[X][Role] Social
I believe this set of choices keeps the focus on Sincerity, which has been essential to the connections Ling Qi's made with other characters in the past. Mischief has been an essential part of Ling Qi's character since the start, even as she's spent less time entertaining this side of her character as the story has progressed. Ling Qi has grown to have far stronger relationships with spirits than normal as well. Both Mischief and Spirits would be useful in a social art, as has been explained by others.
I am unsure about whether I want Mystery or Secrets in our remaining two keywords. I do not think making Secrets a focus of a defensive art is a good idea for Ling Qi. Even if we could make it work with Sincerity, it may divert focus away from the theme of Sincerity in the arts we receive. Having Secrets in an offensive art, on the other hand, would be well suited for Ling Qi. Ferreting out secrets relates well with Ling Qi's character and past experiences.
The same issue applies to Mystery, except the other way around. Mystery is suited well for a defensive art, as Diomedon has explained. Offensively, however, I am not sure how it would work out. It could involve using the mysterious qualities exemplified by the art to cause one's opponents to reveal more information than they normally would or make decisions they otherwise wouldn't. Arts using the Mystery keyword might cause opponents to lack the information they need to make the correct decisions. Mystery in an offensive art could also be related to the idea of "solving mysteries." Ling Qi has some experience with this in the past. Socially, however, this seems like an inferior version of ferreting out secrets. I don't think it's likely for Ling Qi to run into situations where there are drawn-out mysteries that can be figured out purely socially. My main issue with Mystery is that I'm not sure exactly how it would be used in an offensive social art.
Both Secrets and Mystery are good keywords. There are just issues with both of them in my opinion, so I'm not voting for them for now.