I've been thinking her health issues were just anemia, and the time limit was something relating to her mother. Said as much earlier when she mentioned the anemia, herself. But the official line for her transfer back to Kyushu is probably 'health' as a simpler excuse to placate most folks.
Ohhh... hah... I should have seen that coming. Of course we're getting Mikage, the 'old man' girl, in on things if Kyushu is involved. Time for an excursion arc?