DesertFox -
But it made me think she's got a lot of secrets that she isn't willing to reveal to me.
She probably does and you're better off not knowing. What good would it do? Her other 'secrets' are likely to be more variations of the lies, addictions, crimes, overall sickness and dysfunction that is her life. She is a very damaged person and it's sad, it really is, but you can't change or cure her. Your friendship and help haven't changed her yet, right?
She needs professional and spiritual help but she has to seek it for herself.
In the meantime, it's hurting you to keep the relationship, sporadic though it is. I suggest you stay away and think of the experience as lessons learned.
I was involved with an addict/alcoholic in the 70s. I almost married him after a period of sobriety. I was with him through many sordid, frightening events and times, like you were. I won't go into the whole thing but leaving him was the best decision of my life.
Stay strong and stay far away.