Lori Spengler she is the main antagonist in the first film Happy Death Day, but the second dimension of herself in "Happy Death Day 2U she is more a heroine than a villain, in this timeline she decide to help Tree and not killing her.
She was portrayed by Ruby Modine
After Tree is knocked back into another dimension, she goes to her dorm room to confront Lori about the poisoned cupcake to which Lori tells her that there is no cupcake meaning that she is not the killer in this timeline.
Later, while spending time with her now alive mother Julie, she sees a news report about John Tombs, Lori's scapegoat in the previous dimension, being taken into the hospital. She goes there to kill him by grabbing a fire ax to which she is caught by a police officer and arrested. As he's escorting her out the Babyface killer appears and kills the cop before pursuing Tree. She still thinks it is Lori until she turns up in the elevator behind her and grabs Tree to safety. Lori takes her through an area that is under construction, but the killer appears and kills Lori by stabbing her in the chest. He then chases Tree up the stairs, but she manages to trip him down. He gets up quickly and catches Tree on the roof. She loses her balance and falls to her death.
After being revived in another time loop, Tree goes to the lab and tells Ryan Phan and his friends Samar Ghosh and Dre Morgan that she has to die multiple times in order to find out who the new killer is and close both time loops so they can fix the reactor. In a suicide montage, she electrocutes herself in a bathtub, drinks drain cleaner, dives into a wood chipper, skydives in her bra and panties with no parachute (while flipping the bird and deliberately landing in front of Carter and Danielle), and also jumping to her death. However, when she wakes up again, the added trauma from her constant dying continues to take its toll on her, and she collapses in Carter's arms before he takes her to the hospital.
While in the hospital she sees Gregory Butler (whom she had an affair with in her home dimension) but he does not know her as she not one of his students and is instead having the affair with Lori. She tells Butler to get Lori away from Tombs while she is escorting him to the operating room. Tree escapes and knocks the cop out to take his gun. When she gets to the OR, Lori is already dead. Tombs appears behind Tree, but she shoots him twice. She asks who freed him, right before the killer appears and tries to grab the gun out of Tree's hand. She sees a tank of flammable gas and shoots it to kill them both.
In another time loop, while having a tender moment with her mother, Tree once again sees a news report that Tombs has escaped again and has killed Lori, Carter and the cop. Tree realizes she has to stop the loop from closing, or else Carter and Lori will stay dead. She grabs the car keys and rushes out, trying to reach Ryan but fails as he and the others are gearing up for the reactor to go off. Tree then drives toward an electrical plant and charges into a box just a second before the reactor goes off once again killing herself.
Tree is revived and goes to tell Ryan the algorithm, but this time, she has decided to return to her original dimension. Bronson and two security guards then come in to seize the reactor a whole day earlier than planned. Needing an urgent plan to steal it back, Tree gets Danielle to pose as a blind French student to distract Bronson while they take his keys and get into the office where the reactor is before taking it back to the lab.
Before returning home, Tree goes around trying to get closure. She approaches Lori and sincerely talks to her about ending her affair with Gregory, as she knows that it is not worth it. Tree then gives Lori a hug. She then goes to Danielle's room to say how wrong she was about her, only to find Nick Sims emerging from the bathroom with nothing but a towel, and Tree sees that Danielle sucks in both dimensions. Finally, Tree goes to have the birthday lunch with her parents, but she asks David to let her have a moment alone with Julie, which is basically Tree having one more final moment with her mother.
Tree goes to the hospital that night to save Lori. She gets to the room with the cop's gun and kills Tombs before he can attack. The ladies run out but are cornered by the killer. Tree correctly guesses that the killer here is Gregory, wanting to silence Lori for the affair. Before they can run, Gregory's wife Stephanie shows up to shoot Lori. She hands the gun to Gregory to kill Tree, but he shoots Stephanie first. Tree runs and grabs a weapon, and Gregory goes after her. He gets Tree in a room containing a high-powered magnet that he does not even notice, but Tree does. She holds a screwdriver as he draws his gun on her, but she has some final words for him: "You're screwed." With that, she turns the magnet on, and Gregory gets caught in it by a metal chair. Tree releases the screwdriver, which runs through Gregory's chest, killing him.
Carter shows up, and he and Tree help Lori onto a stretcher. Tree tells Lori she is sorry for how things turned out, and how she wishes things could be different, even though Lori does not know what she means. Meanwhile, Ryan, Samar, and Dre have gotten the reactor up and running, but Bronson and the guards are trying to stop them again. Samar and Dre hold them off as long as they can while the reactor turns on. Tree tells Carter again that they are together in the other timeline, and they share a kiss right just as the reactor reaches its mark, a mere second before Bronson can pull the plug.
Everyone returns to the correct timeline in the beginning where Ryan, Samar and Dre were activating the reactor. After Tree asks Carter about Danielle (as he was dating her in one of the time loops) he confusingly asks "who?" Tree becomes happy that Carter remembers her now and pounces on him to make out with him before the film ends.