After spending years of my life being beat within an inch of it and called every degrading insult in the book, I wouldn't be a very strong, open-minded trusting person. And it isn't as though they've spent much person-to-person time together. I think it's been under 5 years since they married, and Riftan isn't a gentle man.
Ok? I'm not passing judgment on whether what she did was right or wrong, I'm saying things would've played out far differently if the Duke hadn't been able to move her to another location where he had control.
Was she weak? Yes. Is it understandable WHY she was weak? Also yes. But she also was very well aware of what was waiting for her if she went back home with him, and ultimately it was a poor judgment call because she voluntarily walked that path. What's frustrating to me is that she had a decent amount of character growth up to that point as a mage, and it just got flushed away at the first indication of a problem. She earned a lot of goodwill from her selfless act saving everyone and really didn't capitalize on it... I had hoped she had gotten at least a bit smarter about how to take advantage of power/influence on others.
You quite literally are passing judgement. You keep calling her weak when in actuality, she's strong. You also don't seem to know what it means to be a victim of abuse/a toxic environment. Her decision to go to her father's home wasn't because she's "weak" or because she's "stupid", she's literally in survival mode and she's going with the choice that her trauma convinces her will give less pain. She's not weak, Maxi hasn't had a safe space to practice healing and to reprogram her brain to stop being in survival mode. If anything, Maxi is strong because she tries to better herself even though she hasn't found a way to heal and even though she's in survival mode. Also, you mentioned how her character growth got flushed away at the first indication of a problem, that's called a relapse. Maxi has accomplished a lot in the year she's been away from her father but she's experienced 22 years with him and since she's never truly faced him or herself, of course she'll relapse. Maxi has spent more time running away from herself than she did truly accepting herself which is why I said "grew" because success doesn't fix trauma.
I personally think assigning blame in these sort of situations is meaningless. You can always reflect and learn how to better handle similar situations. But whats the point in blaming yourself? I don't think there have ever been more useless words spoken than "This is all your/my fault". Cause you can honestly pin the blame on anyone you want and make some excuse of why its their fault (examples below). And those words are only used to hurt someone.
Examples: It's the princess' fault for not noticing something was wrong. It's Riftan's fault for leaving Maxi on her own. It's the Duke's parents' fault for raising such a POS. It's Ruth's fault for teaching Maxi magic. It's the knight's fault for being cornered in the fight. It's the monsters' fault for existing. It's the people's fault for living in a village near monsters. It's the Magician Tower's fault for not sending a magician to help. It's the Duke's heart's fault for not stopping before the Duke took Maxi. It's the sun's fault for giving life on the planet.
You see how silly it gets?
What...? Where did I say she was "stupid"? I said she was "weak," but I'm not saying it to say that she sucks; I'm referring to how she is literally set up in the narrative. She stammers, she flinches, she second-guesses herself. She's weak by design because she's made weak by the abuse she received at home. She can absolutely still find a sort of strength in managing that trauma, but ultimately outside forces have made her narratively weak... which I am assuming is the whole point of all of this story, to explore her healing and growth of character from that involuntary weakness.
If you are reacting personally from this, if you yourself were a victim of abuse at some point, then I genuinely am sorry that it happened to you. No one deserves that. But I want to emphasize again that I am not passing judgment on her as a *person*, but rather my reactions to how the author is choosing to handle the narrative of weakness.
It's also a valid point about the relapse, but admittedly I can know what relapse is and still be frustrated at it in a story, simply because I was really rooting for her to figure out a clever solution to her predicament.
It may be meaningless, but it *is* also pretty realistic for Maxi to blame herself... it's pretty natural to blame yourself for something even if it isn't logical. But it's also objectively true that had she refused his demand to return home *something* different would've happened. Would it have been better? Debatable, but it might've been potentially more successful than acquiescing immediately.
I personally had been hoping she might've turned the goodwill and loyalty she might've earned from saving everyone into a shield against her father, like having those people protect her from undue treatment, but unfortunately the story seems to have kind of handwaved away all the awe and respect that everyone was initially showing her.

I mean, Maxi is right, if she hadn't been weak and just gone home with her father this wouldn't have happened. Like he would've thrown a fit maybe but not being in his home territory and having her knights back her up would've stopped him from taking her.
BUT, the Duke is also a giant steaming pile of shit and such corrupt entities like that really need to stomped out, so his head needed to roll at some point. The other sister could always take control of the region instead under new leadership if the Duke is executed.