Fiona - friend or foe?

[A Cousin]

I just happened upon this thread and as we re-watch into S4 I have been thinking more and more about Fiona. For me, Fiona is a friend. While I agree that the main reason for her being there at all was Adam, I thought she brought an original female dynamic to the team - something in between Zoe and Ros - and an interpersonal plot line that was worth exploring and well executed.

I have lived a similar kind of high intensity relationship for the first 10 years of my married life so I can relate to the Adam/Fiona dynamic. While admittedly not nearly as dangerous, working and living in each other back pockets with no real home creates a intense and different kind of relationship. The adjustment came when that life stopped.

I have also kind of felt that Fiona was a work in progress that was interrupted. She felt a bit like an unfinished novel that had to be wrapped up quickly and plausibly. I have always wondered if the producers/writers knew where the Fiona plot was going to go from her introduction - they do hint at it early on - or if it went the way it did out of the necessity of OS's personal life at the time?