Hi,
That is something that she will NEED to be mentally prepared for. The Oxy is long out of her system and when she goes through withdrawal, it will be from Methadone. I can tell you that it will be a lengthy and difficult withdrawal.
I think you mentioned yesterday that she was participating in meetings but stopped? That is a shame because she will need help from others who can help her get through this and show her that there is another way. If she has not confronted the issues that drove her to use drugs in the first place, she will have little incentive to stay clean.
I know this is difficult for you and painful to watch your child go through this. I pray for you both.
Please make certain that she is ready before she begins the next leg of her journey.