I'm thinking she's someone(or something) that's been split across time and space, or that all of her incarnations are echoes/messages (like the cracks and the bad wolf thing) sent through time and space, with the payoff happening at the 50th anniversary.

I'm also wondering about the "friend" who brought back Strax. It was mentioned but no further details were provided, so it's probably foreshadowing for a future storyline (otherwise they could have easily explained it by saying that this Strax is from Vastra and Jenny's timeline before the battle of demons run happened).

BTW, I'm also miffed that Moffat seems to be high on the fairy tale things, where problems can be solved and enemies are defeated through love, or friendship, or sadness or hope, or because someone remembered. I would much rather things get solved because of the doctor's cunning or through some other sci-fi plot device.