Not long after Celestia has found out that Luna had acted against her wishes she decided that Luna should have the right to serve the kingdom she created in the past as long as she would also do her duties for Equestria.
While this double workload is tiring, Luna is content and she misses out on nothing that has to be done, neither for Plenaris nor for Equestria.
But many Equestrian ponies fear another rebellion of the younger Princess and demand that Celestia either keeps her close or imprison her again.
Not willing to do either, she now faces the frighteningly large rebellion while her sister has fled to Plenaris.