DIL... No... he was not practicing the "do unto others" rule. As you know, we cannot control or dictate how others act or what they do. It's hard to be kind to the alcoholic/addict. We are so angry much of the time, that we usually focus on retaliation or ways to stop them from using their drug of choice. I just try to always be kind, no matter how he acts towards me. At the end of the day, I am accountable to only myself and my God.
First and foremost, you must come to accept that their actions and behaviors are not in your control. If your MIL is going to spend her money on booze, then there is absolutely nothing you can do about this to change her mind. Her change MUST come from within herself.
Many here will tell you that you would benefit from attending Al-Anon. I agree. However... since you are "new" to seeking help for your own behaviors and feelings, then I would suggest that you also check into whatever family programs might be available to you through your local rehab or treatment center. These programs are usually free to the family members or anyone who needs to LEARN about the disease. Personally, I don't think you can adequately and rationally face this unless you first have some knowlegde about the illness, itself. The treatment center will teach you everything you need to know. Then you can seek help for yourself by attending Al-Anon. This is just MY personal opinion, based upon MY personal experience.