The One Thing That Prevented Jenny from Returning to Doctor Who
The Doctor's daughter had a very complete arc.
Georgia Tennant seems to be connected to Doctor Who in the most fascinating way.
The daughter of Peter Davison, who played the fifth incarnation of the Doctor, Georgia had several guest appearances on the sci-fi show, one of which, as Jenny, the Doctor's daughter, brought her worldwide recognition and acquaintance with her future husband David Tennant, who was then playing the Tenth Doctor.
And although Georgia appeared in various Doctor Who-related episodes and projects throughout her career, her character never returned to the series.
Jenny was the title character of the episode The Doctor's Daughter. In the episode, the Tenth Doctor and his companions arrive on the planet Messaline, where the inhabitants use clones to supply their army, which is in a constant state of war.
They create the female clone from the Doctor's DNA, and this becomes another point in the Doctor's character development.
Though Tennant's Doctor initially refuses to accept Jenny as his child, the character grows on him as the episode progresses, and he begins to teach her his own moral principles, leading to the girl sacrificing her own life to save the Doctor.
The final scene, in which the Doctor becomes a father mourning his daughter's death, is probably the most heartbreaking moment of the entire series.
However, after the Doctor leaves Messaline, Jenny has a kind of regeneration, apparently inherited from her father, which heals her wounds. She ends up leaving her homeworld to explore the universe and enjoy her new-found independence.
Although the character of Jenny only appeared in one episode, Whovians loved her and wanted to see her cross paths with her father again. It would have been nice for the Doctor to know that his daughter was alive and well.
But despite getting her own spin-off audio series, the character never returned to the original show. And that was probably because Jenny had completed her arc in the episode. As Georgia Tennant explained to Radio Times:
"I felt like [Jenny] was kind of a perfectly formed character... she disappeared off into the universe and that felt like a lovely full stop – with a little question mark after it. And that was nice."
Born as a clone who was supposed to die soon in an endless war, Jenny developed into a badass character independent of her background. And that story was probably good enough without being continued.