My wife was a patient at a methadone clinic for 3 years. If the clinics are ran correctly I guess they could do some good, unoftunately, the one that my wife went to was not. Anytime she talked to a counselor about a problem the answer was always the same...you need to up your doasge. She started the program taking 30mg a day and by the time she stopped going she was up to 130mg a day.
She went to an inpatient rehab facility and was told that methadone is worse to detox from than heroine. If there is any way you can talk her into something else...do it. Methadone may work well for someone that really wants to change their lifebut most people arent that strong.