Steve Rogerson wrote:
This was such a sudden change, especially after the episode Bounty, which was one of Jenna's best episodes, that one suspects it was part of a deliberate decision to elevate Avon's role. Whether this came from pressure from the actors or from feedback from viewers, I suspect we won't know. However, from now on, Jenna's role is reduced. She had a good first season but a bad second season, the reason quoted for Sally Knyvette's decision to quit the show.
It's possible to suggest an 'in-series' explanation, in that Jenna did apparently betray the crew in Bounty (although she did use her position to save them in the end). Perhaps this incident decreased her standing with the rest of the crew, and led to the rise of a new second in command, Avon. He was the only alternative: Vila was clearly unsuitable, Gan too passive and Cally susceptible to alien influence.
Best wishes, James