Her whole pivot into even-more-than-normal overtly reckless behavior three episodes after the supposed precipitating event felt very abrupt, and the scene where she talks it over and appears to resolve her issues with Ma’ah felt rushed, almost forced.

Agreed. It's tricky injecting serious notes into an all-out sitcom and I'm not sure it worked as well this episode as it might have.

The Sito Jaxa makes reasonable sense as a backstory component, but I found it distracting and it does add to the “small universe” syndrome that expanding IPs risk falling into

Again, agreed. Lower Decks has as much (more even) blatant fan service as Picard season 3, although because it is a comedy I find it more forgivable and less grating than I did in the other show. That said, "Lower Decks" is my favourite TNG episode, so appreciated the Sito Jaxa callback for that reason (and it was a nice way of connecting this series and the episode it was named after). As long as they're not foreshadowing her return. That would be very very bad. They thought about bringing her back on DS9 but wisely refrained. Keep your hands off Sito Jaxa's corpse McMahan!!