Right, I’ve got it. I want the Doctor to have had a daughter on Gallifrey prior to Susan as always assumed, but he blocked his memories of her cus losing her was too painful or whatever. This is the woman in the cloak that he hallucinated, and — mostly for confusion and throwing a cat among the pigeons — she is also played by Georgia Tennant née Moffett. It is never explained if she looks like Jenny because she is her, or Jenny looked like she did because she was born of the Doctor like the original. Either way The Doctor’s Daughter becomes infinitely more traumatic.
The Master discovers the Doctor’s wiped his memories of his own daughter and it freaks him out, (it is ambiguous as to whether she’s both of theirs), and this is the worst minute he’s ever had before the next one when the Master discovers the Doctor has also blocked off all his memories of him too.
And it turns out we’ve got so many Eastenders actors because this is what the show has become.