It's the delivery. Normally, if someone is making a joke, they would be smiling instead of deadpan. Yes, deadpan delivery is a thing, but Ivy doesn't seem like a person who has that style of humor. By itself, it might be nothing, but putting everything together, it does lead to a possibility that she is a bad actor that has orchestrated some of the shit happening in the story. For example, isn't it a possibility that she had some deal with Axel to get him closer to Lena in exchange for the Wildcats thing? Of course, it could also turn out to be nothing sinister like that.Or she simply is making a joke about it. It's hardly uncommon for people to make fun of the lovey-dovey shit people in relationship go on about, along exactly these lines, that it makes them wanna throw up, without any malice behind it.
But Ivy is not a good person whichever way you slice it. I say that most characters are multifaceted with good and bad qualities, but if I try to name a good quality of Ivy as a friend (like in real life and not a porn game), I can't really find it.
At best, she is a materialistic onlyfans thot that tries very insistently to shape her friends into adapting her values. At worst, she is a manipulative "queen bitch" that likes to play around with other people. In all likelihood, it will be somewhere in between, but the starting position of those two endpoints are quite skewed towards the negative side.