2548

2548 was a pivotal year in the life of Bernice Summerfield. She lost both her parents within six months of each other (PROSE: The Evacuation of Bernice Summerfield Considered as a Short Film by Terry Gilliam, Return of the Living Dad), making her an orphan by year's end.
Though it was conceivable that she lost her father in December '47, the likelihood was that it happened during the first half of '48. During the Battle of Bellatrix, Dalek forces engaged the Earth Alliance Spacefleet at Bellatrix. At the end of the battle, Admiral Summerfield's battleship, Tisiphone, fell into a spatio-temporal rift and was transported to Earth in 1963. Benny was seven at the time. (PROSE: Return of the Living Dad)
Later in the year — at some point between Benny's birthday and 21 December — Daleks attacked the Earth colony of Beta Caprisis. Claire Summerfield was killed. Survivors of the attack were evacuated to a space station aboard the luxury liner Star of Lucknow. (PROSE: The Evacuation of Bernice Summerfield Considered as a Short Film by Terry Gilliam) Benny was eight at the time. (AUDIO: The Extinction Event)
== Behind the scenes ==
Just to be clear, most of this is calculated knowledge, rather than direct statement. The starting point for calculations is 2540 because that year is directly stated in Just War as her birth year and because Just War goes to great lengths to invalidate the year given in Falls the Shadow, 2422, as being a year following a different calendar. 2540 is later confirmed by Genius Loci, because that audio has her getting her M.A. in 2562 at the age of 22.
So, 2540 is clearly her birth year.
We know she was seven years old when her father disappeared because we're told that in Return of the Living Dad. We know that she was eight when her mother died, because we're told that in The Extinction Event. We further know that the two events were six months apart because of The Evacuation of Bernice Summerfield Considered as a Short Film by Terry Gilliam.
Since six months before 21 June is 21 December, the earliest time she could have lost her dad was 21 December 2547. However, neither The Evacuation . . . nor The Extinction Event characterise Benny as having just turned eight. Thus, she probably has been eight for more than ten days, meaning that the Battle of Bellatrix more likely occurred in early '48 than late '47.