Yeah, I don't particularly care for the first one either. The second has potential. I like the detail about her legs. Instead of "the only thing," try "all." It's shorter and helps the reader's eyes focus on the meat of the sentence.
I'm with daniL--question pitches don't work that well, imo.
Ha, this a good example of how you can't please everyone. Welcome to the feedback loop; it's come around full circle! See, a month ago, me and a few others thought that "All Sulla", and up top me and a few others thought that sounded like a name, and suggested to change it to "the only thing" or something else, and now the suggestion is to change it back to how it was originally.
I agree that the questions don't work for this one, and like "The only thing Sulla knows about her past is that she was buried alive with enough magic in her blood to damage her legs." best, although I still think it was a bit off. To me, the second half sounds like she would damage herself, but I don't know how that would help her.