Use TK to pick up and throw the canisters at the large gun. To avoid the huge blast, go to the back of the room. You will notice some glass things that popped out of the floor. Get behind one of them. Once you destroy the huge weapon,
Marlena will fight you. TK the canisters and throw them at her to defeat her. Note: The canisters will refill after you use them all (they must all explode). Also, make sure you are on the side that she is on.