Honestly, I think you attempted to do what you felt was justified. Usually with new sick policies, a manager is supposed to let all employees know with a verbal acknowledgement first, then for you to understand and sign it- either in person or electronically.

So sending out a randomly-timed email to a personal account makes her also accountable, and it can get messy- such as your situation. And yes we may accidentally put an abundance of mixed messages in the trashcan.

I will say though, your mother shouldn't have intervened. You are 17, still young, but do have to create some backbone/independence when defending your sick day, as you are entering the workforce and sometimes can be taken for granted.

All in all, I think with what you had, you did what was justified.