After the Mission Priority: Thessia, you’ll have access to the Mission: Grissom Academy: Emergency Evacutaion, this Mission is best completed before the Mission Priority: Citadel II, because there are some consequences for not doing so.
Choice: Grissom Academy
Grissom Academy is a school for the Alliance’s brightest students. The project here, is mainly aimed at Human Biotics, and how they can control their powers. If Jack survived the Suicide Mission in Mass Effect 2, she’ll be in charge of the students here. Also, depending on your choices from the Project Overlord DLC, David will also be here.
Choice: Grissom Acadaemy completed
If you complete this mission, you’ll rescue Jack, and her students. This will grant you them as a War Asset. Also, you’ll be able to carry on your Romance with Jack if she was your love interest in Mass Effect 2, mainly in the Citadel DLC.
Choice: Grissom Acadaemy not completed
If you don’t complete this before the Priority: Citadel II mission. Jack, and her students will captured by Cerberus. In the Priority: Cerberus mission, you’ll find a log telling you that she was brainwashed, with her students being used as experiments. Finally, at the end of it, you’ll have to face off against her as a named Cerberus Phantom enemy.