Originally Posted by BobJM
It's not that important. She's not in this story, she's either left the Brotherhood/dead. It honestly doesn't matter.
And, should her character be needed again in a future flick, a simple scene or line of dialogue can be created for explanation. But that can all be done later, doesn't need to be seen in DOFP.
After the ending to FC, any explanation like that will come off as completely cheap.