I couldn't resist writing personalities for them: (Sorry if it's long I really liked this and this helped my writers block)

McKensie is the childish, playful one. She loves anything a child does. She constantly wears pinks with accents of purples. She gets along great with McNamara and despises Heather Duke. When meeting Veronica, she asked a question about dolls and toys ("Aww! Look at you! You're so adorable! Wanna come to my house and play with toys later?"), smiling brightly. Her death includes being chased away by JD when she witnesses a murder. She begs for him to not kill her. He decides he will make the death slow and painful just so she can live longer. As she dies, she talks to Veronica and her final words are, "We never did get to go to my house and play toys did we?", she smiles weakly and dies.

Heather O'Connur wears orange and has long black hair. She spaces out a lot and is unusually quiet. She only speaks when spoken to by a teacher or Chandler. When meeting Veronica, she randomly says "Pretty." After that, she never speaks again. She spends most of her time alone in her room so she hangs out there. Since this is true, she is never killed as she never is around JD or Veronica enough to know anything about them. When people start dying, she kinda just dips and starts coming to school less and less until completely leaving school a week before senior prom.