The four-time national champion secured the top-two finish she needed to guarantee her Team GB spot but then sat and watched domestic rival Holly Bleasdale set a new 4.71m British record with a brilliant display of pressure jumping.
In contrast, the 28-year old - who made her Olympic debut in Beijing but failed to qualify for the final - could only clear a best of 4.26m, over 30cm down on her personal best from last year.
"I had mixed emotions initially because I didn't jump very high but it was enough to come second and I suppose that is the whole point of the trials," she said.
"It's a massive relief because you're expected to do well and I was expected to make the team and it just adds more pressure.
"It was strange competition and tough one but now hopefully I can just focus on jumping a lot higher because technically I'm jumping well.
"In training I've jumped a couple of 4.50s so I feel I'm worth so much more but I haven't done it in competitions. It's about doing it when it matters now."
Dennison's performance at the Alexander Stadium means she will not travel to this week's European Championships in Helsinki, the event in which she finished sixth in Barcelona two years ago.
"That was a fall back option for me if things didn't go right at the trials, thankfully I don't have to worry about that now," she said.
"It's a major championship but the focus is obviously the Olympics and I can just work on things in training now and try to stay fit and healthy.
"I'll probably have two more meets before London and then it's all about the Games.
"The last week has been a bit scary with the trials looming but now I can relax a bit and enjoy the Olympic build-up for a few weeks."