Jack was experimented on by Cerebrus forces but, managed to escape. She also became a criminal and was held at a Blue Sun prison but, was rescued by Commander Shepard and then became one of his squad members. Jack had an aggressive and hostile attitude. She didn't get along with Mariandia. Jack also becomes a biotic instructor by Mass Effect 3 and if you save her squad then they are drafted for front line duties. If you do not rescue Jack's team in time ,then Jack will become a phantom and you must defeat her. Her tatics are the same as the average phantom except she insults her opponents.