If SHE arrives on the DAY in NEST, then the missions PEACEFUL DREAMS and KEEPING BALANCE have failed. Try to see if SHE can be reasoned with, but back off upon encountering hostilities. Get EGG and your group away from HER. EGG will most likely already have realized the last remaining way to oppose HER are the ROCKS, if not help make her. Get EGG and your group safely to the ROCKS. After gathering the ROCKS, your group should be able to hatch EGG, and hatched EGG then should be able to use the ROCKS to defeat HER.