Trouble understanding a woman’s behavior towards me and my girlfriend

Hello there! I am not sure if this is the right community to ask this question, but I am sure a lot of you will be able to answer. This one is directed to females if that’s alright. I’m a 26M that’s finishing up his master degree. I’ve noticed a new female student throwing these aggressive flirtatious looks at me a couple of times now. While I think that she is very attractive, I am in a 5 years old relationship with an incredibly sweet and loving partner ( 24F ) and am therefore not interested in engaging (on a side note, I also don’t understand what response is expected form a single man to that, as it just makes me feel a bit uncomfortable tbh; would also be curious to hear). I think I made my stance clear by simply looking away immediately when I see her and made sure she sees me with my partner. The other day my girlfriend and me ran into her and as soon as she saw me, she quickly looked at my partner, swept her from top to bottom with her gaze and threw a smirk at her that she described as “challenging”.

I am pretty confused (and frankly curious) as to how I should interpret this. Please explain and feel free to give any tips.