iluvtheatertrash said: "Laura's leave of absence was due to continued complications from her accident during Into The Woods. There's a lot more to it that I'm not sure whether she ever went public about, but her accident in ITW and the surgery that followed wreaked a lot of havoc on her body and life for quite a while. "
She eventually did go public with everything, as she had started to gain a reputation, both within the industry and amongst the public, as someone who calls out a lot and was unreliable. As I recall, a big part of the problem is that the injury was misdiagnosed as to its severity and thus not properly treated at the time.
In regards to her casting in the show, I agree with many others that she was wrong for the part. They cast a rising young soprano and tried to force her into this weird pop-mix that didn't showcase her best talents. The role truly called for the sweet girl-next-door type, which is not what I think of when I think of Laura Benanti.