From the 2013 video where Geoff got the Londonist team to race against each other on the London Overground, Vicki takes a shortcut on the Victoria Line and from ~4:20 onwards we can see Vicki's height relative to that of a London Underground 2009 stock carriage (Figure 1).
An archived Wikipedia article dating back to 2018 contained a diagram of a 2009 tube carriage will be used here to determine the approximate height of Vicki. The diagram is 303 pixels tall, judging by the video screenshot in Figure 1, it appears that Vicki is approximately 189 pixels tall compared to 303px for the tube carriage.
That's 62% of a tube carriage's total height, or nearly 1.79 metres tall if going by the height according to the Wikipedia page on the London Underground 2009 stock. She is over 5'10", and only looks small compared to Geoff's gigantic frame.