How to help a loved one get off Xanax?

Someone I love very much has been taking 4 mgs a day for 12 years. She says she's finally ready to taper off and quit but than something stressful happens and she goes from 2.5 right back to 4. Her doc is no help at all-he's the real pill pusher type and once when she finally got to 2.5 after months and was doing good he TOLD her to bump it back up. She is a danger to herself and others behind the wheel and her finances are going to crap, as well as her relationships. Today I finally intervened and took her pill bottle and began rationing them out to her. She went nuts at first and threatened to call the cops but later broke down and admitted it had to be done. How quickly can I safely bring her down in dosage? She didn't want to take any after I took the bottle. She had taken one at 11 am and I practically made her take a half at like 6 pm but by 10 pm she started shaking and getting sick and I got her to take a full one. She has agreed to listen to me and maintain a constant level in her bloodstream by taking a full one when she gets up and 3 half-pills equally spaced through the day thereafter. I know the basics to avoid severe symptoms but how quickly do I taper her?