Sadie (Fanfare for the Common Men)

In the proper timeline, Sadie was a huge fan of the Beatles. She met the Fifth Doctor at one of their concerts in 1963, at which the Common Men also performed; she called them "a bit naff".

When Lenny Kruger altered history so that the Common Men became big in the Beatles' place, her allegiances were to the Common Men from their very start in the mid-1950s, when they were still small. This was mostly down to psychic manipulation relayed to everyone on Earth from amplifying equipment in the Pfannkuchen. In this timeline, she teamed up with Lenny to help him make the Common Men the biggest band in the world.

To do this, they used his time travel technology, to manipulated in time and get it to suit their needs, and some form of psychic amplifier, to get people to artificially love the group. She helped with much of his crimes, and would have been arrested and charged as an accomplice to Lenny's supposed murder of James O'Meara, before the Fifth Doctor reversed the damage she and Lenny had done. With the original timeline restored, she returned to normal. (AUDIO: 1963: Fanfare for the Common Men)

Behind the scenes
The name Sadie alludes to The Beatles song Sexy Sadie, one of the songs Lennon wrote during the band's India retreat that appeared on The White Album.