She didn't want to leave the country because of her former lover and her family...
I know ner reasons, but she eventually got over her former lover and doesnt visit her family much and she could visit if she married the king too.. like marriage is a serious matter especially in those times when getting divorce is hard and life after that even harder.
Maybe she wanted to make it her decision and not be the witness of her fate.
But if you ask me the way she handle this was pretty dumb.
She should have married the king. Why did she choose regan ,, i will never understand the fl thinking.