I feel like we're talking past each other here. If she could have stopped Onnotangu, she would have. Since she didn't, it means she couldn't, and therefore she wasn't his equal.
And if it were just a case of her wanting to avoid violence, she wouldn't have made Hantei fight. Instead, she thought when her huband was unfit for rule, their son should take over. In other words, a hereditary monarchy.