I dont understand what you see as why?
I think the fact she has not run again indicates she has not for this period been interested in being a candidate, and possibly ambivalent about getting elected again as an MNA or MP.
That may or may not include 2015. But there are not going to be a lot of possibilities in the NDP. There has been a lot of loose talk around here about possibilities of a number of seriously contested nominations for incumbent MPs in 2015. There may be in 1 or 2 one-off cases... but it isnt very likely, and its not most people's cup of tea about how to run for office.