Okay first of all, leaving all these idiots aside, the MC is too good that she’s actually stupid.
When they make love, why didn’t she reveal herself? She won’t be doing it out of malicious intent, rather it’s Yuriel’s and Etssen’s fault. Here’s what would happen :
1) Etssen knew she was there but still did it, so she has proof that her concubine is cheating on her, and that gives her reason to get rid of him.
2) SHE HAS PROOF THAT Yuriel is touching her concubine, AND LIED to her about her having no relationship with Etssen. This will give her enough reason to drive her away or even kill her, for lying to a royalty.
Tsk tsk tsk