For Briar it definitely was when she moved to Unova after disbanding Team Flare. For her, being part of Team Flare was not a bad experience per se, what was really awful for her was what happened after it no longer existed.

When she moved to Castelia City, she stopped doing scientific work and had no money to afford the luxuries she was used to with Lysandre. And that, too, her fiancé had just died for his ideals of a beautiful world that was never going to work. At this point in her life, she blamed herself for the downfall of Team Flare, since she was the Commander, she blamed herself for "not working hard enough", for "not trying all the options", and specially for letting Lysandre die.

In Unova she kept a low profile because she was also being chased by the Interpol, and started working at a theater; she always loved the arts but could never dedicated her life to them to favor her scientific career, but since she was now trying to start a life from 0 and as far away from science as possible (so people don't suspect her), she became a performer. But still, even if she was doing what she always wanted to do, being so depressed made her unable to enjoy any moment of this.

Overcoming this took her years, but it started when she moved to Galar when she agreed to help Rose on some scientific project he had. Her story in Galar is basically her journey through a grief she kept bottled up for years, alongside her finally coming to terms with the downfall of Team Flare, including (but not exclusive to) finding out that she wasn't the one to blame for Lysandre's decisions, among other things.

It is true that Briar overcoming all of this was done thanks to her own efforts, but she knows she couldn't have taken the first step without Rose and Oleana, and she always thinks they saved her life.