First off I would never recommend methadone to ANYONE. OK so I know you didn't ask about methadone, I just wanted to get that out there. As for the OC habit and suboxone, I can't be sure. The only time I went on suboxone was to get off of methadone, and while it worked wonderful for me when I was on it, coming off of subs was a nightmare for me. Some people have great success with it and some don't. One thing you should keep in mind is that suboxone has a much longer half life than OC, meaning that if she ends up getting bad withdrawal from subs it will last a lot longer than OC withdrawal, and that sucks, a lot.
Honestly I recently had great success coming off OC with a fast taper. I let myself get into withdrawal and then I would bite a small piece from an OP 60, probably about 10-15mg. I did this every night for four days and it actually worked. The small dose at night let me sleep and stay rested. And beyond a bit of fatigue and some aches in my legs, the daytime was not bad at all. After four days of that I felt confident to stop, and I did.
A couple things to make her chances of success better, at least IMO. First you should ask the suboxone doctor if he would prescribe a small one time amount (like a week worth) of a long acting benzo like Klonopin, or even just a benzo of any kind. Also you could ask him for a week of a sleeping aid like Ambien. Make it clear to him that she is serious about quitting immediately and not just looking for more drugs. Next get a box of Immodium AD (anti-diarrheal), and a big bottle of Ibuprofen or Aleve (OTC pain relievers), and finally maybe some Benedryl (OTC sleeping aid, if you can't get a prescription sleep aid). After that, if possible take a small vacation. Find a hotel with a nice heated swimming pool and use it daily. Go out and eat some good food, have sex, drive places, walk around. A change of pace and scenery can make all the difference during withdrawal. Also for me I had great success with swimming during WD. It's easy, fun, comfortable and it exercises all of your muscles in a smooth fashion. Priceless really.
And speaking of price, if a small trip sounds expensive to you it's really not at all compared with a drug habit or a maintenance program or especially a professional rehab. We drug users are always finding ways to mentally justify the money we spend on drugs, but we always seem to get stingy when it comes to getting clean. Honestly any money you spend on everything from the doctor to the medications to the vacation will pay itself back in a couple weeks of not spending money on OC. Best wishes.