Your sister needs about a 4-7 day detox to ween off the xanax. Xanax is a very strong drug but pretty easy to get off in a detox center. Depending how much she drinks, she may need a full month detox for that. Drinking and xanax is a really bad combo and dont let she stop one or the other without help. She could try to ween off the xanax with your help, by handing them out to her and giving her a quarter to half mg less each week but if she is not willing then the detox center is your best chance for recovery.
I went thru that exact thing......drank, did xanax....the first thing I did was quit the drinking....it was easier because I still had the xanax......BUT, quitting the xanax was a different story! When it came time to take it, my body would shake and the anxiety would be horrible. I had to go to the ER one time....the gave me IV ativan....calmed me down, and sent me home with a prescription for ativan. They told me not to stop taking it until I physically arrived at detox which was about 3 days later. There, the weaned me off using phenobarbital....tool 4 days, and I felt great....gained weight too from the plentiful food :) Benzo's are tough....I think they would still take her without insurance....there are other arrangements that can be made....or contact a doctor....maybe she could be slowly weaned....Good Luck and Bless you...