I just re-watched her introduction the other night (in the two parter “Silence in the Library / Forest of the Dead”), and something weird occurred to me. (I’ll try to keep the spoilers to a minimum, but no promises.)
It occurs to me that she’s meeting the Doctor in what is the first time for him – and it’s David Tennant. But when we see her again (in “The Time of Angels / Flesh and Stone” two parter), it’s Matt Smith. The thing is, she immediately recognized Tennant – and expected him to recognise her – although this is the only adventure we ever see with the two of them together.
Which implies that somewhere in the expanded Whoniverse or the fan-fiction Whoniverse, there are tales of the two of them together again which, at least in as far as the two characters meeting, have some basis in the actual canon of the show.
Just a little something to think about, folks 🙂