i was not going to say it may be...................
cos we all are wrong in the end.

she must have knew who it was....... the master.

more likely it was a dalek.

Dalek. She knows that they're supposed to be dead. Hell it might be Dalek Caan, she knows him!!

Well unless he's learnt to fly, I don't think it is the Matser. She is looking out of a window high up over London. So most likely flying Daleks, of which she only believe there is 1 left after Caan escaped, hence her shock in probably seeing so many.