Horn, you're to be commended for your ability to process all that you have going on. Thank you for sharing what sounds like a lot of different dynamics.
I'd start by trying to adjust/limit my MIL involvement in my life. Boundaries are healthy.
Ten year old girls are a challenge in the best of families. Patience, breathing, time outs (for you, not her so much). As you get more sobriety time going on, you will get stronger.
You have many people in your corner! Stay the course!