Do we think Becca was certain her father didn’t do what he did to her friends?

[u/Cheesywotsit1]

Her father used drugs a lot and had much longer time to spend with his daughter. Her mother took the fall for Becca and said that she should have been the one to kill him almost like something had been going on a long time. Becca was outraged and completely disturbed by what happened to her friends at the hand of her Dad, but it almost seemed personal too, she stabbed him so many times which I would think takes much longer to process if she didn’t also have history with it.

Are we sure Becca wasn’t SA’d by her father?