Hello perpetuum, welcome to Psych Central.

That is a real worry but the thing is, you cannot do this alone. If you feel that your friend is in immediate danger you can actually call the police so that she can get to a mental health hospital. Or you can contact mental health services direct, their number will be in the phone book.

Here is a list of helpful mental health numbers Telephone, Hotlines and Help lines | Psych Central

You friend needs to help as soon as possible. Let us know how you get on.