They could have even done it in Sonic Frontiers, despite having already made the decision to alter her personality by that point. They really wanted to push a character-driven narrative in the game where everyone reevaluates what their relationship to Sonic is and that would have been the ideal time to just come out and confront the issue.

Have her reflect on how she spent her younger years believing that she could twist Sonic's arm enough to finally make him her's but getting nowhere with it because he isn't into that kind of relationship with the people he knows and coming to accept it. I originally thought Frontiers had already missed the boat by that point, despite the opportunity presenting itself, but even doing it in retrospect would have probably satisfied the need for character development. Instead they just let that opportunity pass by too.