So this movie I saw when I was little (around 2002) that my mom loved to watch involved this girl who’s grandmother treated her badly so she killed her by letting all the air out of her oxygen tank. Another part of the movie I remember was the girl getting a job at this office (she killed the first choice they hired so she could get the job) and she rubs peanuts on some bread to give it to her coworker (who’s allergic to peatnuts). Once she starts asphyxiating, she dangles her epi-pen in front of her and watches her die. I can also remember her cutting her grandmothers hand and putting it in a jar but I could be mistaken about that part. The movie was in color, my mom had it on VHS and it may have came out before 2002. My dad swears it’s an old lifetime movie but I’m not so sure. It’s not ‘Devil in the Flesh’ and it’s not ‘Secretary’ cause I don’t remember Rose McGowan or Maggie Gylenhaal in the film.
try Red Riding Hood (2003). Not an exact match, but many similarities to what you describe.