I think she was full of herself and thought everybody paying attention/devotion to her only. That’s why her behaviour towards Lotte went from indifference to slight irritation as Lotte interacted with the MLs and the MLs began to be somewhat accustomed to Lotte and her silliness plus paying mind to Lotte’s presence. Or something like that. I’m not a 100% sure.
she is going to show it in chapter 131. there was a party at Lottes house and Ibelin came and talked to lotte in privat. that's when she became mad at Lotte. then they showed her past where she had loving parents who adored her and that she was liked by everyone. at some point there was this one girl who thought Ibeline was two-faced.
i have to wait for the new updates to read what happens after that :(
it isn't until chapter 131 that Lotte realize Ibelin`s true nature.
Arwin starts to realize that he doesn't really have feelings for Ibelin. It's just the original plot of the novel. he starts to realize it in chapter 120. Lotte and Arwin kiss in episode 127 and after that they become lovely around each other.