Now as you know, I love to draw certain parallels between the way Liz behaved as a schoolgirl and the way I'm certain Elly must have behaved when she was young. The example I love to use is that when Liz tells her that is convinced that nobody could ever possibly like her because of her stoopid nose and how it made her look stoopid and ugly and unlikable, Elly's response is a bromide about how the only ugly thing on Liz's face is a scowl born of irrational, invincible self-loathing. Since we're not dealing with a very bright person, it's sort of clear that Liz never seems to have ever made the connection between her inability to see the obvious when it's staring her in the face and the fact that she never had a very wide circle of friends growing up.
As you will recall, I love to state that Elly's social life back in the sixties must have run along the same lines; we already know that she made a ridiculous nuisance of herself throwing herself at a crush who regarded her as, at best, a joke. We can also therefore assume that Marian had to spend a lot of awkward nights listening to Elly cry that she'd be an old maid because she was ugly and nobody liked her and all the other teenaged crap Liz spouted. Given that no plotline ever revolved around old friends from Vancouver ever visiting and that none of her trips back to the coast ever had her look forward to getting in touch with school chums, we can also safely assume that she wandered the hallways thinking that the people she never made the effort to talk to were all stuck-up haters and, dare I say it, that she couldn't be convinced that there was one boy who everyone was sure had a thing for her.
Let's combine this basic inability to understand how people around her think with Jim and Marian's aggressive need to impose a strict double standard on her in the name of respectability; what she sees is not two dim, well-meaning people doing what's expected of them to the best of their own lights but instead two big meanies letting a younger sibling who should take a back seat to her because she was there first just because he was a boy. No matter what she did or how sincere she was, Phil always won everything without even trying and that wasn't one bit fair; therefore, she has to shackle Mike to get back at Phil for always, always making her life miserable by winning when he should be a good boy and not only let her completely dominate his ass but also to apologize for existing. Odd how that's what Mike wants Liz to do, isn't it? Guess self-absorbed, vengefulness isn't just for Elly, ain't it?