It is likely, due to the setting, that she was "sold off" as a daughter from a high-ranking family, something that since it is the emperor, she cannot refuse.
But her father even hesitated to marry her off, and ask her opinion if she want to refuse it but she gladly accept the marriage offer. And it was the noble who insist The Emperor to marry hence he set up those condition, he doesn't even care who his partner is.
Oh yea, I reread. Actually, isn't it likely that she just wanted the plot of the story to happen and to see it happen or something?
If you want a stable and peaceful life, why bother become a Queen at all? You have intelligence, status, and appearance, even if you laze around all day, you won't go bankrupt. Even if you have no ill intention, doesn't mean others won't.