I've just found this forum and this is my first post. After some reading, I thought I'd share my situation and ask for advice.

I'm engaged. She has a 9 year old girl and a 15 year old boy. I have a 10 year old daughter. She is very, very protective (in general) of her daughter.

Stepdaughter and I get along generally quite well. She's a great kid, and I like her a lot.

The problem is that she knows she can get away with anything with me. Generally, she's really good at making the water works flow when she gets in trouble by her mom, but with me, she just ignores me, walks away while I'm talking, hears "different" things than what I actually clearly said, and "forgets" what happened. It's all nonsense... she's manipulating me and the situation to get what she wants.

Nearly every time (with occasional, RARE exceptions), if I call her out on something, her mom just jumps in and explains why I'm wrong. Example:

I had brought home an antique musket and left it in the living room while the family was gone. They returned early, so I came home to put it away. The daughter makes jokes about playing with the gun, and I immediately responded (my own gun safety training kicked in) and I said "We don't make gun jokes ever". Her mom immediately, in front of the daughter explains why she didn't know, why it wasn't that big of a deal, etc.

Every time I've tried to talk SO about how this undercuts me, or how it's important for us to present a united front, the SO blows me off or blows up at me.

A few minutes ago, while doing laundry, I called the daughter down to get her stuff. She got pouty about having to work (a strike that would have been immediately dealt with for my own daughter) and then pretended not to hear me when I said "come right back, there's more". I called her back and told her clearly to come back.

She didn't, so when I went up to where she and her mom were talking, I looked at her with raised eyebrow and she gave me that "Oh shit, is he going to call me out" look. But I realized I was literally so nervous about dealing with massive fallout that I was literally shaking like a leaf.

If my SO has little to no interest in dealing with this issue, and I'm not wanting to live in an environment where I'm scared to death of a 9 year old, what the hell do I do??