I truly believe that you are never wrong when you honesty & truly put the kids first. I absolutely believe that is your intention here wtbh; no matter how or why you're triggering, that part comes through loud & clear.
I think she's not only protecting the addict, but herself. She doesn't see how ANY of this is related to addiction, focusing on how you are attacking her parenting instead. And I agree with you, it's definitely a situation where we can easily see that an extreme codie is as sick as/if not more so than the addict themselves.
All in all, sounds like you're going to lose a friend no matter how it goes from here. Or - maybe not. Don't count out that one day she WILL have her awakening & decide to break out of this dysfunction she's living in. We all have different "bottoms" after all.
For you, examining the unexpected triggers - like dealing with the police - could be GREAT recovery work that you couldn't have gotten to any other way. I'm sure you feel completely off-balance today because you aren't comfortable with this "new normal" yet & you probably have a lot of anxiety & adrenalin left running through your body needing a way to be purged. Try some exercise, deep cleaning, journaling, etc.? (((((HUGS)))))