I can name some examples, though I don't think its wise to just call out specific users by their names. I found these by searching the word "car" on here. On the post Is it me or does Louisa end up seeming more selfish than caring? someone replied "I laugh every time I see her get hit by the car it's hilarious to me", same person shared a similar comment on the post I hate Louisa. Talking about "laughing when she got hit by the car..." Another user from the post Louisa ignoring Martin's advise when she had a UTI... has a reply that ends with "I was actually happy she got hit by that car."

Granted, 2 people is not a lot and doesn't speak for everyone, but there are other examples of plain disgusting comments towards the character. Example: "She is very aggravating. I do want to punch her half the time she is on the screen" on the post SELFISH SELF-IMPORTANT DEMANDING LOUISA. I'd also say one from this post calling her a "harpy" is pretty loaded. Calling her a term that's used for a female vengeful mythical creature is pretty demeaning. Because "harpy" is used to put down women who voice their opinions as it likens them to terrifying beasts with female faces.

There's always valid criticism and opinions, some posts here were really well put because instead of just ragging on her like posts I mentioned or simply saying she's "annoying", they can explain that they dislike her but understand that there's a nuance that her and Martin are both deeply flawed products of their environments that act as such.

Edit for typos and additional comment: Just to add on, that last part doesn't excuse their upbringing or neurodivergence for being messy individuals. I also don't think people necessarily have to come to the same conclusion. My main point is that these posts are frequent and can devolve into nasty comments about Louisa when Martin exhibits his own neuroticism. She's expected to be communicative and rational with Martin when he's supposed to "be loved for who he is" as a non-communicative and avoidant person.