Shriek If You Know What I Did Last Friday the Thirteenth

While in her house alone dimwitted teenager Harvey "Screw" McAlister (Aimee Graham) is attacked by "The Killer". While being chased, Screw accidentally runs into a bug zapper and her face gets electrocuted. The killer, feeling disappointed that he was not the cause of her death, lights up a cigarette, leading to the melting of his Jason Voorhees mask into a Scream mask. The next day, new kid Dawson Deery (Harley Cross) signs up at Bulimia Falls High School, meeting up with a new group of friends including Boner (Danny Strong), Slab (Simon Rex), Barbara (Julie Benz) and Martina (Majandra Delfino), to whom Dawson takes a liking, though he is not sure if she is a lesbian. While the group discusses the death of Screw, they remain certain they are safe in school, not noticing the chaos that surrounds them, including a nuclear bomb being built and the killer attempting to murder a student.
The group encounters EmpTV News reporter Hagitha Utslay (Tiffani-Amber Thiessen), who is covering a series of murders, having already written a best-selling pop-up book about them, and accuses Dawson as the killer. They then meet Barbara's brother Doughy (Tom Arnold), an inept security guard who recently lost his job patrolling a shopping mall and is working to find the killer; however, he believes Screw's death was a harmless prank. As the group talks, they do not notice Hagitha's cameraman being murdered. As the day progresses, more and more students are murdered. While in class, each of the group receives a letter from the killer, revealing he knows a secret about them. Each of the group recalls a time when they were drunk-driving and hit a deer, before dumping it in the sea. This event leads each to keep their own secrets; Martina not giving her grandmother laxatives, Boner accidentally causing his brother to be killed in prison, Slab smoking his uncle's ashes, and Barbara accidentally removing the "do not remove tag" from a mattress. Meanwhile, Hagitha and Doughy continuously flirt with each other. As the group meets up, Dawson gets a letter too, as he was in fact run over by the others while dressed up in a deer costume when a hillbilly forced him to wear it and do salt lick. The hillbilly died in the explosion. The group decides they should spend the night in a secluded house, so they each arrange to go to Slab's after school. As the day progresses, each of the group members are attacked but manage to escape. The killer confronts Principal Interest (Coolio), but he electrocutes himself in a bathtub.
At night, everyone goes to Slab's party. Boner takes an unconscious girl up to a bedroom so he can lose his virginity. The killer attacks him, but Boner suffers a heart attack before the killer can murder him. Martina goes over the rules of a parody movie, before Barbara is chased outside by the killer. However, Barbara suffers an allergic reaction to bee stings before the killer can murder her. As the rest of the party people leave, Martina makes a move on Dawson, before they find Slab has abused steroids, causing him to explode. Martina and Dawson then are chased by the killer, as Hagitha and Doughy play strip poker nearby instead of investigating the murders. Martina and Dawson defeat the killer as Hagitha and Doughy arrive. The killer is revealed as Hardy, Doughy's "evil twin cousin", whom Doughy is going to let get away with the murders, but Hagitha accidentally shoots Hardy before leaving Doughy for a pizza boy. Martina, Dawson and Doughy leave the house, where they find Boner is still alive and finally loses his virginity to a nurse. As Martina and Dawson leave, they get a call from a new killer.

Question: What did Martina not give her grandmother?
Answer: laxatives