dave ramsey classes are a must for anyone wanting to get their financial life in order. i would take it as a family so that its not about "her" but its about all of you. as americans, we ALL spend more than we should, we ALL make money mistakes, and we are ALL contributers directly to the financial problems in our country today. it is OUR fault. so the solution lands on our shoulders. its too bad that most people just keep spending like teenagers without a plan, which keeps wrapping the problem up tighter and tighter.
go to dave ramsey's website, find a class near you, or write to them to try to get one near you. you could also do the home study, but with an actual class, you get more interaction with others, which increases your accountability, and gives you more motivation and ideas than doing it alone.
the next thing i would say is something i think dave ramsey says; let her fall on her butt. obviously you want whats best for her, and her son. if she needs to fall on her butt, then let her, and make sure that her son is provided for. she might need to fall on her butt 3, 4, 5 times but let her. im guaranteeing shes not breastfeeding if shes going on bar binges, so i doubt thats an issue here (if it is, obviously make sure that you can support that while letting her fall on her butt.
things like giving her only baby food or formula as your form of assistance. you know? do SPECIFIC things that allow you to know that you are providing for him, but not padding her greedy pockets. diapers. clothes. (and remember, for your own good, 2nd hand clothing, couponing, watching online deals like money saving mom, etc can help you while you are assisting her son)
after a few times that her phone gets shut off or the phone calls start, and hopefully she will take the class with you, she should start putting together the pieces. everyone wants to provide the best they can for their children, so i know in the back of her mind she WANTS to do better. she just probably doesnt know HOW to start. dave ramsey will give everyone guidelines, or steps to follow, to help get started small, and gradually work up to being self sufficient, self insured, etc etc. its great that shes still relatively young and can figure this out before SHE has to retire.
some of the most important steps are NOT going into debt any further, CUTTING UP all credit cards or store charge cards (even IF they are always paid on time - its BS to have them, especially when you are going to let her fall on her butt!), and step #1 is to put 1000$ into a savings account and DONT TOUCH IT. step # 2 is paying off ALL debt except a mortgage. step #3 is putting away 6 months of living expenses. knowing those three steps alone will at least give you a guideline of where to start while you are searching or waiting for a class to start. im sure dave ramsey's website will give you a lot of help; a budget, a solid ZERO BASED budget (where you literally plan for every cent BEFORE you spend any money) is a great tool, and a must have. its harder than you think though, so be prepared to work together on this.
above all, have patience, love and understanding. this isnt the time to be "a parent" and nag or whatever. try to do it with love and understanding, treat her the way you would treat a friend; because you would never fully support a friend you dont pay her bills, but if the kids were starving, you can provide for that if you so choose to your ability.
i hope that makes sense.
prayer also helps.