She fighting for survival in hostile environment, and she using every tool at her disposal. She manipulating, lies, act like victim and scheming, but she clearly motivated by her fears, not hatred. Regarding "stealing husband" emperors have concubines, it is what it is. We may dont like it, but no one force Sovietsomething (i dont even care to remember this guy name) to take concubine and neglect his wife ostentatiously. So why blame Rashta for that? And we dont know all circumstances regarding her first baby yet. I would not rush judgment here. Please remember that she believed her child is dead, and may be too scared to reveal truth to emperor.
There also many miscommunication, and Navier seems to be poor tactician. She totally ignores her enemy-Rashta, even when she clearly realized that Rashta is blackmailed. Navier could take advantage of situation and crush her, but instead she only display cold and hostile attitude while Rashta fears and paranoia to grows more and more. And please dont get me wrong, im siding with Navier and wish happy ending for her, but still feel a bit sympathy to Rashta, as she seem more tragic then villain.