addicts are messed up in the head, and she is almost certainly trying to wipe all traces of you from the flat. If she sees something in the flat that reminds her of you, it will be a painful reminder of what she’s done, and addicts don’t like that kind of guilt.
If her children are using with her, then you are definitely part of the problem and not the solution. Addicts do like to group together, it validates their own crappy behaviour.
Talking to her family, you can’t predict her family’s response and however they respond is not your responsibility, is it? Are you on good terms with them? If so, you are perfectly within your rights to go speak to them, if only to convey how much you’ve loved her and tried to save your relationship.