"Unless you give us some time to return our guest to her proper universe."

It is of course possible that the Doctor was later able to return to our universe.

"There's no way for me to return to my universe."

"As a practical matter, we will still be unable to return to our own universe, sir."

But if you are to return to our universe, the only means of doing so is by changing that nature.

You just wanted me to return to your universe and see your Earth.

And somehow, we must return the Shadow matter to its rightful universe.

We'll let them return to their own universe and report what we do to intruders.

The heroes eventually learned the truth and they were returned to their own universe.

How she returns to her universe has yet to be divulged.