truancy is against the law - as is a parent allowing a minor to harbor in thier home in order to be truant. and, you as the parent are the responsible party if anything would occur where your daughter got into trouble
you might consider contacting your local sheriff and explaining the situation and that these adults are allowing her to be there and that you would like to have the sheriff remove your daughter or provide an excort for you to retrive her.
if you get into a confrontation, of course, you can be charged criminally - and even without a confrontation they can call the police and have you arrested for trespassing. so best to make the contact with the sheriff to see about an escort.
once that is done, you can go to the court and file for a restraining order against the 18 year old and the parent - stating they are a danger to your child's wellbeing and health and welfare because they are allowing her to be truant in their home.
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