Dolly (The Crash of the Elysium)

Dolly was a human woman who had a history with the Eleventh Doctor.

Biography
The Eleventh Doctor met Dolly, and the two of them once intended to go to Bognor, but accidentally ended up on the Moon, making Dolly the first woman to visit it, with the Doctor later referring to the Moon as Dolly's Moon.

Dolly was later met by a group of humans while on an adventure involving Weeping Angels and the spaceship Elysium. After they saved the Doctor and made the world "a bit safer", he sent them letters profusely thanking them, in which he mentioned his past with Dolly, saying that she "amazing things in her time", before the humans in the group were even born. (PROSE: Hello!)

Appearance
The Elysium being pretty reminded the Eleventh Doctor of Dolly. (PROSE: Hello!)

Behind the scenes

 * It seems that Dolly was meant to be an unique companion of the Eleventh Doctor introduced in The Crash of the Elysium. However due to precise details about the immersive experience being scarce, it is hard to find online documentation of the character, let alone verifiable fact.
 * However, the short story Hello!, framed as a letter from the Doctor, which was given to the participants of The Crash of the Elysium, does mention Dolly and some details about her.
 * Dolly was played by Kathryn McGarr in some showings of The Crash of the Elysium.

Information from invalid sources
Dolly was later left at a fairground in 1888, where she encountered a group of humans led by the army who had been sent back in time from the 21st century by the Weeping Angels; the group had found out about Dolly not too long prior, having found a picture of her enclosed in the Doctor's supposed will retrieved from inside the Elysium.

Dolly explained to the group that they had to return the TARDIS to the Doctor within five minutes by locating it and inserting the TARDIS key they had with the artron energy that they had been imbued with after their journey through time. (STAGE: The Crash of the Elysium)