Pennie, 32, made her Team GB debut in Beijing but four years later narrowly missed out on a place at London 2012 to team-mate Lizzie Neave.
Just over three years on and she reversed that decision winning the recent GB Canoeing selection trials to secure her place on a four-strong squad of canoe slalom paddlers for Rio.
"As soon as I missed out 2012 I was thinking about Rio," she said.
"I always wanted to get to 2016 but I had to respect the fact it might not happen with only one place in my class and the great paddlers we've got in Britain.
"I accepted that I might not make it going into selection and that probably made things more relaxed for me.
"It certainly gives you confidence when you've come through such a demanding selection process, when the pressure is really on and everything is at stake.
"After the trials, Lizzie had missed out and I just had to give her a big hug when she came and congratulated me because I'd been there and I knew how horrible that feeling is. It hurts really bad but you will come out the other side and life is okay eventually.
You could have forgiven her for wanting to avoid the London Olympics but attended every canoe slalom session as a fan, watching from the stands to fuel her determination for another crack in Rio.
"I was never going to avoid the Olympics, I knew too many people competing and I wanted to be around," she added.
"Watching the opening ceremony on television was a proud moment for the country but it was difficult for me but seeing it drove me on for Rio."
Pennie admits there are some regrets with her 16th place in the K1 class in 2008 but eight years on is much more experienced paddler, winning a world silver medal in Maryland last year.
"It's great selection is out of the way and the next eight months can be fully focussed on peaking when it really matters in Rio," she added.
"I was only 25 in Beijing and I'm a very different paddler eight years on."
Sportsbeat 2015