She got sold by her mother. It also turns out that the Marquess needed a new wife since his first wife died of an illness
Even though she have to marry her husband, he was never cruel or abusive to her so... I know it's bad that she was sold, but at least he wasn't a total bad guy. ╮(￣▽￣)╭
It doesn't seem like she disliked her husband either. She seems to have cared about him alot, but probably saw him more as father figure.
I mean it's pretty obvious. Her older brother is a piece of shit. Threaten her to give him money, that is more than enough for me to conclude she was bought. Also the second chapter.
Why did Shuli have to marry that old dude ?