[b]It could be totally unrelated,[/b] but the FWC's grimoire talks about a "she" that is hunting for a single perfect time line. This basically means that they arm and train gaurdians to try and win the war while "she" secures the one timeline that does not have war.
The Stranger, along with some other characters we probably don't know of, are time-travelers. Every time she disappeared in the game she was shifting through time. She guides you on your journey so you follow a set path. This path is the best one from her experience since every other time she's tried it's fail due to a choice that was made. So yes, I do believe she is a time-traveler.