I know you are all angry with rashta but on the other note she is only doing everything to survive and even to survive compfortably.
I mean, she was a slave (maybe born as one) and treated worse than anything.
And now, after having a comfortable live, at least a little bit, she is forced to do anything she can to be the ONE woman.
One of the first things the empress said to her was, that she will see a lot of other mistresses coming after her and for her that only means, returning beeing a slave.
You may all hate her, but if you were in her situation many of you would act the same. Sure, the noble lady did not hurt her, but she was not fond of Rashta, so why should she let her live a nice live while beeing shunned by everybody.