Actually, I am wondering how much do we actually have a right to judge or hate on Rashta. From what we know she was literally a slave, she doesn't have any education and her child was stolen from her (or even killed). I am nearly sure, her previous owner raped her. To say it shortly, her life was absolute shit with no rightful way out. The Emperor was her only ticket to get out of.
Just about anyone who wants to live would have probably done the same. The only time we can't fully justify her actions is when she is hitting on Hailey. Even here, we can say that the emperor would probably have a change of heart and toss her - so, as to not get back to her previous lifestyle, she needs a plan B.