First off, she has no real idea what the pretty girls actually thought of her if they actually thought of her at all. If she were to go to a high school reunion, she'd have to endure being told something along the lines of "Well, it's your own fault, really. When you weren't so tentative and shy that you gave off the impression that you thought people would bite or something, you stormed down the hallways scowling like being Elly Richards was the worst, stupidest thing ever. Blaming us for your lack of a social life is silly...especially since the problem is far closer to home."
This would be futile because no one is ever going to tell Elly that she's misjudged someone or that she doesn't know what she's talking about or going on around her. She is going to look at what she did to Martha and assume that Marian did the same thing to her only Marian was wrong to do so like always. It never occurs to her to reconsider the idea that her mother didn't really like her, not REALLY and wanted to make her life worse all the time or that she doesn't know who Martha is or that being a vindictive idiot because she blamed the wrong person for her lack of a social life is really a very bad thing indeed.
The problem is that the same Elly who acts as if she has to be invited to join a social circle or whatever nonsense belief Liz has to hover at the periphery of playground life gloomily wishing that people would be her friend has spent her whole life being surrounded by a certain cultural stereotype without realizing that it exists and it affected her life. This figure is known as Papa Wolf, Knight Templar Father or Listen, Punk....you lay one hand on my little girl and they'll never find your body. In Elly's case, this entity is referred to as Dad.
Since I don't have her tendency to gloss over Jim's worst traits because he liked to undermine his wife for fun and profit, I have no illusions as regards his tendency to threaten boys that scared him. Elly is right that a parent of hers actively conspired to disrupt her dating life in an attempt to protect her from perceived threats. She's just wrong about which old person did so. This ignorance leads to Martha's suffering.