Blue Balliett Books
I'd like to suggest the books "Chasing Vermeer", "The Wright 3" and "The Calder Game" by Blue Balliett. They involve two kids (a girl and a boy in Vermeer, with a second boy joining with the second book) who solve art related mysteries using math, writing, textual analysis and good old fashioned boundry pushing. The books themselves have codes and clues imbedded within them. I think these would be a great addition to A Mighty Girl because they show girls and boys working together as friends and the perspective shifts so we get to hear from all of the kids, not just a single central male character.