Liara T’Soni is an asari that is over one hundred years old. She spent fifty years studying Prothean technology before meeting up with Commander Shepard in Mass Effect. Liara did appear in Mass Effect 2 but only as an NPC. It’s two years later and she is on the planet Illium and rumor is that she is working for the Shadow Broker.
The newest DLC for Mass Effect 2, Lair of the Shadow Broker, allows Liara to join your party and head after the Shadow Broker. It seems during the two years that Shepard was missing, Liara was trying to get information by means of the Shadow Broker.
No word on when this DLC will be released as news just hit this morning via Twitter. Hopefully we’ll know more shortly.