How do you have someone committed to a mental hospital in Nevada?

My sister is behaving increasingly bizarre and we believe she is threat to herself and maybe others. She has expressed her wish for myself and other family members to die, as well as herself. The police were sent to her house today by us to make sure she was okay, after we received a suicide note via e-mail, but they said she was okay and let her be. She has a history of drug abuse and bipolar and we believe she needs to be in a psychiatric hospital. We don't live in Nevada and we don't know what the law is there about being involuntary commited into a mental hospital. Please only serious answers.