If she is abused and suicidal, either of you can report that (harm is being done to her + she may be a risk to herself, if suicidal) so that she gets the help she needs.

Talking to a teacher to reduce her school time is not enough. She needs mental health support. Good that you don't want to abandon her, as she might take drastic action if she feels she no longer has anyone on her side.

Where does her mom sit with all of this i.e. her daughter's struggles with addiction, her husband abusing her child, being suicidal etc.?