Kicking her out was the right thing to do - for the safety and sanity of your 2 grandchildren. They have the right not to be exposed to that kind of behaviour from their mother.
I know this isn't easy (recently my sister decided to leave her young daughter with my parents and go live with her druggie friends), but there's a saying we have in NA - detach with love. Loving someone from a distance is the best thing to do for you. Don't feel guilty - if she wants recovery, she'll put the same effort into getting it as she does into getting her drugs.