Perhapslove, I'm sorry that you have to watch your daughter choose a path of self destruction. I know that it is hard at the moment, but try to realize at this point in her life all she is worrying about is sustaining her addiction. It doesn't matter how much everyone around her loves her, it doesn't matter that she has a daughter, it doesn't matter that she was given every opportunity to regain a productive and healthy life, all that she was able to focus on was finding a way to sustain being high. In active addiction it becomes impossible to see beyond getting high.
Now that she has picked her path it is time that you pick yours. If she was going to use while she was here anyway, maybe it is better that she left to go use, this way you can move on with your life and enjoy all the good things that you have going on. Sometimes it is better not to have the option to oversee the addicts every move, it healthier for you to have your own space. You have other adult children and so many grandkids (how lucky you are!) that you can spend time with. Try to enjoy the little things in life. You deserve to be happy and not dragged to the depths of hell.
I hope that you can find peace today, and know that you are not alone in this struggle. You deserve to be happy and not consumed with worry. You don't deserve to be lied to, manipulated, or put in situations where you become physically/mentally sick with worry. You are a good person, you did everything that you could do, and now it is time to remember the things that used to make you happy and to do them!
hugs
Maylie