In Two Aces, Rebecca has a breakthrough thanks to Sam - she had been focusing on destroying the team that Rupert loved, but when Sam asked her to attend the de-cursing ritual, pointing out that it was her team, it got through. That's why she attended the ceremony in the first place.
But Higgins betrayed her; he went behind her back, concealed information from her, for the express purpose of acting against her, just as he had done when acting in service of Rupert's affairs.
It was upon learning of Higgins' betrayal that she went back to her office and finalized the return of Tartt to Man City, and Jamie was directly responsible for the outcome of the season's final game.
It certainly wasn't Higgins' intent, but unintended consequences are still consequences.
At the time, she also assumed Higgins was forced to be her Le Fou in the name of keeping his job. She learned in that moment Higgins is his own man, and isn’t as enthusiastic about her mission. I think she would have traded Jamie, or done whatever she could to casually hurt the team, either way.
I think hearing Higgins taking a little stand in that moment changed the way she looked at Higgins and that hurt her, though. I think it’d be easy to think “You had no problem helping Rupert to hurt ME but, you won’t help ME to hurt Rupert without pushback?!” I think it’s foolish and misguided thinking like that on Rebecca’s part, which we’ve all been guilty of before, that lead to her little speech to Higgins about paying his salary, etc. when he quit. She viewed herself as the boss and assumed by paying his salary, she was buying the same kind of sidekick loyalty she thinks her ex had. Instead, they all healed and became much better, stronger people. Ted shook things up enough with his unwavering goodness to give space to grow and confidence to Higgins, while giving Rebecca the grace she needed to heal in order to be her best self, too.