Answer:
hi there!
i believe it is different for each states. the baker act provided emergency mental health services and temporary detention to people who are unsafe because of their mental illness. your sister can be held in there involuntarily for only up to 72 hours.. that is if she wasnt a minor, now for her it is only 12 hours before examination is initiated. you said that you and your family have not been able to see her? as im researching more about this law, it found out that "unless having visitors will be harmful to the person being treated. If a facility wants to restrict visitors from a patient, they must file a written notice documenting the refusal of visitation." which means you guys must have gotten a written notice telling you that seeing her isnt the safest option right now. since your sister is a minor someone must have had to contacted the police/ law enforcement about her..
mental heath facilities have to provide notice to minor patient guardians, no later than 24 hours after admission, they must also document all contact attempts. that notification must be give as soon as your sister entered at that facility.. it can take just about a full 24 hours if the facility have evidence to believe that the patient has been abused.
i have yet to have any evidence that states that they can hold minors without consent of the legal parent guardian, i doubt that your sister was able to even go into that mental heath facility without your parents or someone with the law knowing.
i really hope this help you and i hope the best for your family and your sister!
( here is a photo that might explain the process a little better then i can at this moment )