I am glad she has made a few attempts to get a job. That is good. in my opinion it is time for 'do to get' to be the rule for the house. difficult child wants car. what will she do FOR YOU to get it? If it is in her name, cease paying the insurance, gas, etc... and make those her responsibilities. If it is in your name, take the keys. When she has done something to EARN those keys for the morning, she gets them. If she wants them in the afternoon, what is she going to do FOR YOU to earn those keys? she has feet and people have walked across the US on their feet, so it isn't life and death for her to have a car.
Babies need things. I am sure she thinks that diapers and formula are part of the family groceries. It is time to disabuse her of this. Let the diapers run out. When she doesn't have any, tell her to go buy some. It is her kid, after all. When she has 'no money', offer to drive her to the pawn shop so she can pawn her mp3 player or phone or whatever to buy the diapers. THAT is what broke parents do. The shock of you offering to drive her to the pawnshop will be dramatic. A good thing because it will stick in his mind. It has to sink home that she has to pay these bills if she is his mother. having you and your husband provide all of this for her until she gets off her tushie and 'feels like it' isn't a viable solution.
You need to go and sit down with a social worker at CPS to find out what criteria they watch for in situations with recovering addicts who use whatever she used, and what the criteria for taking custody would be and how to document those criteria. Do this WITHOUT difficult child and ESPECIALLY WITHOUT difficult child'S KNOWLEDGE You are not planning to take custody, you are arming yourself with the info that you will need if she makes unsafe decisions. This is NOT to throw in her face during arguments. It is research to keep the baby safe, PERIOD.
You also need a family law attorney. He should give you info on custody, guardianship, emergency situations and how to handle them, what you can and should do if difficult child disappears with the baby. ALL of this is very different from state to state and even city to city. I know in MWM's situation, CPS must see bruises or marks and have an adult tell them that they saw the abuse to even get a report taken by phone. In my area? We had cops out regularly over one neighbor sending his 5yo out to watch his 2yo child run around after dark - around their unfenced pond. It got a full investigation of the family and parenting and child care classes for the parents and the elderly gma who lived with them. That is a HUGE difference in response and is just an illustration of the differences between jurisdictions and agencies. So go and ask what is involved NOW so that you are prepared later.
As you gather this info, you also do a search on "Do to Get" in the archives, esp Fran's posts. Read what is said about it and how to implement it with adult children.
I want to say that I am well and truly thankful that she is not taking drugs.
That being said, if all anyone ever asked of you was for you to not take drugs, well, they sure don't think you are capable of doing anything interesting or worthwhile or of value, now do they?