We want our families to be supportive, but sometimes they can't be. It sounds like your wife's mom is not capable of maintaining an objective and neutral view of the problem: to be honest, it struck me as odd that your MIL was part of the "intervention" discussion. It really didn't sound like an intervention for your wife, but an intervention to change your mind about the divorce.
Maybe you should try to use your therapist to work some of this out, such as bringing your wife with you to your therapist, or both of you finding a therapist together.
I would say that it is well within your rights to insist that your wife look for a program. She indicates she won't use AA, that's fine. But if she is serious about recovery, then she has the responsibility to find something else: outpatient rehab, inpatient rehab, smart recovery, a program with the Minnesota method. There ARE alternatives to AA. Some alcoholics are helped by a therapist, some are not. She is using a therapist, how much has that ben working for her? If she is still drinking and using, then maybe she needs to get an addiction therapist rather than a general mental health specialist.