Fear for safety of children

I am working through the homework for podcast on blame. In the past I have read about how to deal with ex-wives being hard to deal with (biological mother of my stepchildren) and they give advice but also state that if you are dealing with an addict then their advice is not necessarily valid. Seek help from someone that deals with addictions..
is this what you recommend? I don’t want to blame her, but she has put children in danger in the past (drunk driving at 3x legal limit). I understand that she is responsible for her own actions. And I am responsible for mine. It is much easier for me to know the girls are safe when they are with us. How do I change my thoughts from worry when girls are with her? And if anything happens again, not to feel guilt that I should have done something to keep them from her?