As per a link from Paul Cornell, here's a rather nice overview of the cover art for Virgin New Adventure "Love and War", drawn by Lee Sullivan. Sullivan talks about his excitement at his first book cover and the pictorial creation of a brand new character (and his anxiety about the artwork when reviewers mocked it, but honestly, it's a nice straightforward combination of frocks n' guns and by no means the silliest cover that the NAs ever had). There's also six pages worth of notes regarding Cornell's initial character concepts for Bernice Summerfield, and it's interesting to see how well these held up over the years.
(Of course, once Big Finish started doing stories they leaned towards modeling Bernice on her voice actress Lisa Bowerman, and eventually just started using straight-up publicity photos for their covers. For instance, the celebratory audio recording of "Love and War".)