You are correct in your assessment.
I am sorry you are experiencing such abuse. If you run away and the police bring you back, they know you can run away again over and over. 17 year old runaways are not a first priority with police.
Unfortunately, your host family could be charged with Harboring a runaway, if your mothers calls the police.
Have you reported the abuse to CPS so they may investigate? Have you documented via recording or-note taking the abuse? I am not sure I helped any, but also talk to a school counselor.
Providing general answers are meant to help the poster to understand some complex legal concepts and in no way creates an attorney-client relationship.