Has anybody noticed a trend in the loyalty missions? For the most part the featured character deals with their problem and is able to move on, for instance Grunt feels that he has no reason for being and gets one in his LM.
Miranda doesn't have that same closure, her LM shows us her human side but Miranda doesn't come to a conclusion about her own origins, or deal with her father, and the possibility is still there that Mr. Lawson can always go after Oriana again. Instead of dealing with those problems Miranda decides that it's safer to run and hide. ME3 is the point where she has to face these issues head on, both her personal ones and the ones with Cerberus.
It seems like she has this adventure that runs tangent to Shepard's, whereas Kai Leng is playing the part of
The Dragon in Shepard's story, Mr. Lawson is Miranda's equivalent. They both end up in the same place at the end but the path they take to get there is different.