Alright, let's set some idiots straight. Long Yuyin was an absolutely horrible person in the past life (as far as Nie Lie know, there might be a twist somewhere). We don't know when she became a horrible person or did horrible things, so there's a solid chance she's not worthy of hate at this moment in the new timeline -- and that seems to be what the author's going for. The only thing we've seen from Long Yuyin so far is incredible arrogance. Her first appearance is threatening her clingy fiance and becoming disappointed when he backs off. So she doesn't have any respect for those beneath her (power-wise) or wants a good fight. Honestly, that's pretty average for nobles in this world and it's not like she's anywhere near the worse example of that behavior. And she kinda has to be forceful or her voice won't matter at all in a male-oriented society (see Xio Ning'Er).
Yuyin's first words to Nie Lie is "I didn't expect you to get this high. Hahaha. However, with your lowly status, this should be your limit, is it not?" Nie Li hates her because of his past life, so he fires back, questioning how good she is without her family and calling her trash without their resources. The he insults her bloodline, calls her a bully, accuses her of dominating other people and suggests that her tongue should be cut out and pan-fried. After a bit more back-and-forth, Nie Li challenges Long Yuyin to a duel.
From Long Yuyin's viewpoint, she's just needling someone to get a good fight going or due to arrogance. This is like 99% of the people we see in this story, good or bad. Nie Li is definitely overreacting here compared to his actions towards other arrogant assholes so far, but, from his perspective, this is completely justified given Yuyin's horrific actions in the past life.