Sorry to hear you are all going thru this. Unfortunately the two substances go hand in hand. Crack is very addictive, which would explain the disappearing acts. What would be more alarming is that she is putting herself and others at risk of this nasty virus, so I would urge you to protect yourself and the children. She would then need to make the decision to stop using, however I am very aware how difficult getting off these drugs can be, especially if she is not attending any psychological interventions coupled with the buprenorphine. I hope she has some Naloxone to help minimise any overdosing behaviors.
My advice would be to focus on you and the children.
As for the people she is hanging about with, they aren’t friends at all, however sometimes they can be if benefit especially if she is using. It’s always best not to use alone. Take good care