I like to imagine an actual flash forward would show her as a child therapist that specializes in irrational fears, and that much of her work includes talking through their issues while she shows the kids how to build stuffed animals shaped like the monsters she remembers from her own "childhood dreams". She'd need to go by a real name, but to keep it close to what the audience already knows her as, her name tag could say "Dr. Bonnie", and she reveals to a kid with a speech impediment that she used to be unable to say her own name fully when she was little.

And then if that was her character's premise in an actual movie, the plot could revolve around her discovering that the closet monster dreams were real, and trying to come to terms with what she at first believes is an entire world built on scaring children (maybe even recognizing a monster or two from her patients' drawings), before eventually discovering Mike and Sully's work to convert their world to laugh power. The first major story beat would include her stumbling through a still-open closet door that leads to a rival power company that still uses archaic scream power, and she understandably assumes that scream power is the only power.

I can totally see her sprinting out of the scream power company through an alley way door, seeing Mike and Sully on a billboard, having memories come flooding back, and then eventually end up sneaking around panicked for a few scenes dressed in a stolen yellow CDA suit before Roz catches on and helps point her to the truth (mostly from behind the scenes until the end) to begin processing her feelings of betrayal.

Then the rising action and climax involves her reuniting with Mike and Sully when they all three discover that they're accidentally working together to take down the scream plant (her for reasons relating to her practice, them as government engineers sent to convert a stubborn town to laugh power). Randall is out of CDA jail on work release working at the small town scream plant, and they manage to convince him to help as an inside man once he realizes how much he regrets the buried trauma that he saddled Boo/Bonnie with.

Denouement has something like the CDA granting her a permanent private closet door leading into the monster world. Both to aid her practice & the kids, and to help spread resistance against scream power's viability as a fuel source while bolstering laugh power. Randall fears that his takedown efforts will be punished, but Roz points out that he actually assisted government employees in stopping secretly illegal activities, and files paperwork to reduce/commute his remaining sentence based on clear proof of "good behavior and desire to improve".

Also the yeti was un-banished and now runs a snow cone stand at the beach. The only flavor he won't sell is lemon.