Have you pointed out to her (in a factual way, not accusatory) the differences in the way she's handled these two potential relationships?
It might be beneficial for you both to find out why she treated one differently than the other. I'm poly and my husband is mono, and I know for myself the social conditioning of expecting men to be jealous of other men but thinking two women is "hot" was difficult to throw off in the beginning. It was much easier for me to talk to my husband about my liaisons with women rather than with men back in our earlier days, and it had nothing to do with him. Or it may have nothing to do with gender and be due to one starting as an emotional relationship while the other started as a physical, or something else entirely. I would bet, though, that getting to the root of why she handled it so differently could help you decide how you want to handle it, and it might even help both of you clarify what you want out of your relationship(s).
Pan Female, Hinge in a V between my mono (straight) husband, Monochrome and my poly (pan) partner, ThatGuyInBlack