A bad combination of insecurity, broken pedestal (Navier was (understandably, given the circumstances) frosty towards her when they first met), and Sovieshu being the worst (legit every one of Navier and Rashta's interactions after that first meeting always had Sovi either running interference whenever Navier tried correcting her or confronting him on her behavior, giving her a sense of superiority that caused her to have that unearned belief of being above consequences now that she was empress) alongside Rashta just not knowing better. By the time that final olive branch was extended in the form of the check, Rashta had been already primed to see everything Navier was doing as either a trick or threat, because Sovieshu and her own paranoia convinced her it was. Getting found in that trap by him really was the worst thing that happened to her