Question: Assuming the mother's not arrested despite assaulting the teacher, shouldn't her son be removed from her home given how horrible a drunkard she is and could abuse him?
Question: Why didn't she ask the cops to tell the student she was pregnant with his child?
Answer: Same reason for her actions in the entire episode. She wasn't thinking straight. She recently had brain surgery, her husband left her, she lost her step-son, and now she finds out she's pregnant with a minor's child. All put together spells recipe for an emotional breakdown where no-one can be expected to think straight.
Answer: There is no evidence he did beyond the words of a woman crazy enough to murder her daughter.
LorgSkyegon