I really am leaning on her being Romana, i hope she is, i really feel Romana was the "one" perfect mate in the Doc's life, i have a feeling she may have been olne of his many wives (i know its never been canon confirmed but moffat said in an interview back in the 70's and 80's all british tv was non sexual like that, which is why RTD somehow inferred sarah jane had a crush on tom bakers doc when i saw no hint of a love interest on tv, if anyone was "implied" to be snoggin him as close as the old series could muster it was Romana, Especially in "city of death".)