Well, actually, is she? Her initial relationship stat begins rather low, true, but at no point did she act particularly bad toward the Mc in my interactions with her. The fact that beating Alexander raises her attitude toward you is interesting, I think. While I have the feeling of a rather heated rivalry with Alexander, Abigail does not feel like that at all. She’s a bit cold at first, true, but nothing more.
The way I see it, it seems more like the two actually don’t really know each other and have never really interacted before in any meaningful way. She has an initial negative bias due to her mother, but it’s not even a really strong one if she approves of the MC winning the duel.