Does she? How does Destiny threaten anything? She wanted mutant preservation and set Moira on the path that she is on. Krakoa is something Destiny would support. The only one scared of Destiny's return is Moira and I think its bc her motives arent as pure as we are led to beleive and Destiny would be able to sniff her out.
In continuity though its been months and countless others have been resurrected including Quentin multiple times. Xavier hasnt really given Mystique a good excuse as to why Destiny isnt back. To her it would appear to be cruel