I don't agree with the first one. How could you trust someone who basically took her in as a hostage so easily. It's natural to doubt him.
But I completely agree to the second one. How could she trusted them easily is beyond me.
I think that she joined hands with them as a way to have eyes inside that family. They are suspicious, and I think she knows that, but she's sure or fake-sure that she could handle them if they turned on her.
The sister already backed off from the empress seat apparently, so maybe she's not that bad, but everyone has a personal agenda and it's a risk for both women to be this close everyday. If something happens to either of them there'll be consequences.
I really liked the female character in the first few chapters, but after that I just couldn't understand her. When her husband told her that he would protect her, she didn't believe him. Why did she join hands with the family whose members wanted to harm her?I mean, it just doesn't occur to me how someone could be so stupid.