She had become isolated in her anxiety, she says, feeling every day as if she were trudging through the motions of a life devoid of joy.
But in a vow to escape her comfort zone, she has found herself an unlikely inspiration. And in doing so, has achieved far more than she ever could have imagined.
"You don't grow in your comfort zone, and in a way you're not living," she says today. "You might fail, you might be brilliant, you've just got to try.
"I was going through the motions, each day the same but not really being there. The truth is, you can be fully functioning, but still struggling.
"We need to start normalising mental health, to talk as openly and easily about it as we do physical health."
The 35 before 35 challenge
It seems there is a bucket list for every major milestone, says Miss Barker, delivering a weight of expectation over what constitutes success.
To create a capsule wardrobe by the age of 30, to speak a foreign language, and to be in proud possession of your own home.
Miss Barker, in comparison, felt as if she were failing.
Watching the London Marathon in 2018, the 34-year-old from Wakefield had been struck by the strength of those taking part, and by their stories as to why.
On a whim, she set herself a goal, to complete 35 challenges by the age of 35. But they must all be for her health - be it physical or mental.
"My mental health had been neglected," she says. "I found I was isolating myself from friends, withdrawing. I felt I couldn't get out of the rut I was in.
"With a focus, I knew I could improve my mental health," she adds. "For me, it's about pushing my confidence.
"Even with a marathon, it wasn't about the running, but about the journey to get there."
Raising money for charity and improving mental health
Miss Barker, a former student at Leeds Trinity University where she now works in marketing, has completed a marathon in Honolulu, cycled up Mont Ventoux, and run 127 miles along the Leeds to Liverpool canal.
There has been abseiling and gorge climbing, scuba diving and surfing. But there have also been mental challenges, pushing past her greatest fears to speak on the radio.
"I'm doing these massive challenges, but for some people it could be something as simple as getting out the door, and that's a massive achievement for them," she said.
"Going out with friends was out of my comfort zone, it still scares me. I would rather run a marathon tomorrow."
As Miss Barker's 35 birthday approaches in March, she is preparing for her final task, running, cycling and swimming 260 miles from Kent where she was born, to Leeds Town Hall.
Through it all, she has now raised over £3,500 for Leeds Mind, and for Yorkshire Cancer Research.
"I feel like I'm finally getting there," she says. "But this isn't the end - I want there to be a legacy with a big event every year.
"It isn't a quick fix, but I'm definitely more positive than I was. I'm glad that I've come this far, and for all the support I've had, from family and friends and work.
"It has helped my mental health so much," she adds. "There were times when I wouldn't want to do it, but that's the point in pushing yourself.
"There are still days when I struggle. But I'm more aware of it, because of the journey I've been through."