Following Peter's rescue from the parallel universe, the prime universe Fringe team comes to learn of the Wave Sink Device, the machine that Walternate was attempting to use to destroy the prime universe. They are unaware that Fauxlivia has replaced Olivia, and she works to help the Fringe Division to identify the components hidden across the globe for a similar Wave Form Device in the prime universe. She also gets romantically close to Peter. Olivia is held in Walternate's laboratories in the parallel universe, and given drugs and conditioning to make her believe she is Fauxlivia, and subsequently a willing test subject for Walternate's tests of the powers of Cortexiphan. Olivia slowly breaks this conditioning, and on one trial, is able to cross over to the prime universe to relay a warning to Peter about Fauxilivia. Her identity exposed, Fauxilivia is extracted back to the parallel universe by Walternate's shapeshifters, while Olivia gets help from Broyles to cross back to the prime universe. Olivia is distraught after her return, knowing about Peter's relationship with Fauxilivia. However, after some time, the two reconcile and admit they have feelings for each other.
