Respectfully, her behaviour is part of the problem, the other part is your mom's willingness to put up with it. If the sister found doors locked to her whenever she acted like this, possibly she would vent her anger elsewhere. My parents went through this with one of my sisters.
Call the cops, evacuate the sister from the premises and don't have her back.
Is this my sister talking about the other one?.....Debbie?
she needs anger management