You said they found meth in her system ...
some of the emotional and weird reactions, I highly suspect, may be do to withdrawal symptoms as the meth leaves her system.
(Withdrawal from drugs isn't pretty, for the person withdrawing or for the persons observing it.)
... Maybe your sister will seem better in a few days, when her system gets back to 'her normal'.
If she's adamantly fighting it, your sister may find herself 'restrained' for awhile when moved to the mental facility.
Not a pleasant thought to ponder, but at this point, she needs to be protected from herself.
She's not thinking or acting rationally. She's not capable of it, at this time.
It is by the Grace of God that your sister is still alive.
So then, would seem to me He still has plans for her life ...
... Sorry your family is going thru this.
Notoriously, the holiday season is often a difficult one for persons suffering with mental illness.
Many suicides, and attempts at it, happen during this more emotional season ... unfortunately.