28 days after what starting point ? recruiting cali ? 28 game time from begining ? or other point ?
edit : well, now checked my game, and im on day 29 of game time, and it is some time that i tried and failed to save calis parents, so there must be different time limit.
If her parents died and she has been with you less than 28 days, it's a bug, most likely. Share a save before visiting her village, maybe some dev will understand what happened.