In my story, the main character is being sexually abused by her teacher. Her life is severely screwed up from no father, mother being too busy for her, etc. The inciting event is when the a new girl in her school gets the attention from the teacher in a way that makes the main character jealous.
I want to make the main character snap after multiple small events that make the main character feel insecure about her relationship with the teacher.
Any advice on how to build up anger, tension, and envy to eventually make the main character snap and kill the other girl?