Man, everyone acts different around family than others, so I can definitely relate. It isn’t the same thing for sure, my wife does the opposite and leans on me more when her family is around. But she’s stressed by them, and it changes her behavior patterns.

My kid isn’t my biological kid, and when there are forced interactions with the biological father’s side of the family, behaviors change drastically. Enough so that when they occur, we book therapy sessions for before and after.

I’m different around my family than my friends, or my partner, though not as significantly because I’m older and more centered within myself, so it’s more about minor shifts in word choices and body language, and I have really solid relationships with my relatives.

So you, and she, have to first be able to recognize that it’s a simple, human thing to shift into the behaviors of a given “culture” as you move between them, and that both parties have to learn to acknowledge each other’s boundaries regarding that.

It may help to stop thinking there needs to be a confrontation. While not everyone uses the word the same, it does tend to occur when a similar kind of thinking is in use. The idea that you have to have a specific event where you present a difficulty and work towards a solution isn’t really necessary. One can address difficulties casually, and it often gives better results.

And, there’s also the need to gently establish and reinforce boundaries in a situation appropriate way.

Here’s what I would try next. When there’s a bout of “nagging”, you can just very gently and quietly say “I don’t appreciate this behavior, and I do not accept it.” Obviously, doing this around her family isn’t a good idea unless you’ve tried all other avenues.

You stay calm. If you can’t stay calm, you walk away with a promise to come back to the subject later.

If she can’t stay calm, you are allowed to walk away and state that you do not accept the behavior, but you’ll gladly discuss it later. Or, if you can stay calm, reassure her that you understand family can require shifts in behavior, that you love her, and encourage her to continue in a respectful way.

I promise you, it is vital that two adults contemplating merging their lives legally and socially via marriage have to build the ability to communicate. You have to have a mutually acceptable, mutually understood framework for resolving differences in a healthy way. Even during crises, hell, especially during crises, the ability to resolve a dispute in the moment, that’s something that can save marriages, or save lives in extremis.

You don’t have to make her explain anything, or discuss anything, about her family and why hey behavior changes. You don’t even have to ask, though offering to listen is an important thing. What is necessary for both of you is to be able to establish good boundaries of behavior towards each other. Sometimes, the best thing you can do for a stressed partner is say “no” to reacting to their stress with stress of your own.

A good boundary will help her because she will know that you’re sticking with her, that you see the stress, but won’t participate in unhealthy behaviors. It can help someone learn to overcome that stress and deal with it better for themselves.

I’ve had to do that myself a few times over the years. My wife isn’t prone to unhealthy behavior towards me, but she does sometimes slip into unhealthy behavior towards herself. I won’t give details because it isn’t my story to share, and it isn’t anything that would help anyone else, beyond saying that it isn’t anything horrible, and isn’t anything to worry about.

But I do have exes. And one of those exes is an ex for the same reason you’re presenting. Family history made her want everything to her idea of perfect, which led her to nitpick things. I drew very clear boundaries, including that I wouldn’t be changing myself to please her family, and enforced them as needed. Alas, it needed doing often enough to become a problem, and I actually broke up with her for our mutual health. It was not a pleasant breakup, and I’m usually quite friendly with exes.

Now, obviously, this is based only on your side of the story, and assumes that anything needed to know is present in your post. For all I know, she’s telling you to stop wiping boogers on your pants, and you should obey. But learning how to set boundaries, keep them, and handle disagreements calmly and casually as they occur is always good advice, and those are skills, you have to work at them. I didn’t pop out of the womb all calm and able to think during emotional events, nobody does. So the sooner a person starts practicing, the sooner they gain the benefits.