My friend has admitted to having hallucinations and she has acted very strange lately, what should I do?

I’m fifteen and this friend of mine is thirteen. In the entire time that I’ve known her she’s been a kind, everybody’s friend kind of person. Recently however, she seems to have become much more agitated, depressed, and angry, flipping people off at school almost daily. This was very out of character. I was already worried about her before, and then she admitted to my sister (another girl in our friend group) that she was hallucinating. She told her that she would see entire people in her room and maintain conversation with them. She also said that while she could see and hear them, they could never touch. I’m very scared for her and want to try to help her, but I don’t even know what to do or if she’s told her parents. Any advice you may have about how to approach the situation or get her help would be great.
My friend has admitted to having hallucinations and she has acted very strange lately, what should I do?
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