Internalized ableism is a significant part of Lydia’s character, and if Teen Wolf had a better track record with mental health issues I’d love to see this explored by canon. (I don’t really trust the writers with this topic though.)
I’ve seen a lot of meta about Lydia’s character development since season one, about how she shed her “vapid popular girl” persona and is now owning her intelligence to the fullest. But I haven’t seen so much about this side of Lydia. There’s a big part of Lydia that is still very concerned with appearances, and she knows the stakes are higher now. It isn’t about crafting the perfect persona for school anymore, it’s about whether or not other people are going to take her seriously as a human being.
Lydia knows that being crazy means people stop listening to you. They write you off, they second-guess anything you have to say, disregard your emotional needs, and stick you in an institution when they get tired of dealing with you personally. She has at least one institutionalized relative that she knows of, and she knows that these things run in families, but that won’t be her, that can’t be her, she won’t be like that, she’ll make sure of it. (Except she knows, in some corner of her mind, that she is crazy according to her own understanding of what “crazy” means, and this knowledge terrifies her.)
Lydia’s terrified that she isn’t in control of her own mind, and she’s terrified that if she admits this it will completely discredit her. She hates not knowing how her banshee powers work. She doesn’t want to lose credibility with her friends, she doesn’t want to be the weak or needy one, she doesn’t want to be seen as unreliable, unstable, deranged, unhinged, incompetent, all the other things that “crazy” probably means to her.
So she relishes the things she can control, like her appearance, her intellect, and her relationships with boys. She feels triumphant when Allison, Scott and Stiles experience their post- ice bath hallucinations because to her it means she’s “not the crazy one anymore”. She also distances herself from Meredith.
She’s probably especially afraid to get too close to Meredith, even though Meredith, as the only other banshee she knows, has knowledge and experience that Lydia desperately needs. She can’t risk getting too close, because she doesn’t want to dwell on the similarities between them, doesn’t want to be associated with Meredith, doesn’t want other people to conclude she’s “crazy” too and start treating her the way they treat Meredith. So she takes out her frustration on Meredith, she loses her temper and makes biting ableist comments.
Lydia has a lot going on with her mental health. She has her PTSD from Peter, her grief over Allison, her frustration over her abilities as a banshee, the stress of being on the deadpool and fearing for her life and the lives of her friends. On top of that, a lot of Lydia’s inner turmoil seems to be compounded by her internalized ableism. I would really like to see her confronting her beliefs about neurodiversity and mental illness. Learning that it’s okay to not be okay, it’s okay to have needs that differ from other people’s, learning how to seek out support rather than isolating herself. It would be a really good source of character growth for her, and an important message for viewers too.