Hello Lori,   I will respond as best I can: a teenager with schizophrenia who abuses drugs is a MICA client, someone who is a mentally ill chemical abuser.  She could be doing drugs because she is self-medicating the symptoms of the schizophrenia.   The younger sibling might want to attend a support group for family members of loved ones who have schizophrenia.  She also might want to check in with a therapist trained to counsel teenagers.   If the mother is in denial, it will be more difficult for the daughter with schizophrenia to recover because the mother may not believe that treatment is necessary.  Also: when drugs are involved that should not be discounted.  People who abuse drugs and have schizophrenia are at a higher risk for violence.  Which would account for the animosity perhaps.   So I recommend a support group.  The younger daughter should also feel comfortable telling her parents when her sister is experiencing symptoms, so that the older girl's psychiatrist can be alerted.   Regards, Christina