Fact: Since her brain is hard-wired to never see what's good in her life, Elly seems to not have outgrown the belief that when people criticize her, it means that they hate her and want to see her suffer; this means that she doesn't get better and things and never develops anything like a sense of responsibilty.
This leads us to what sets her at odds with Mike, Lizzie and April: the fact that she envies them because at least they don't have a heartless monster like her own mother who can only find fault. Despite the fact that early on, she had occasional glimmers of awareness that she was the same sort of mother inflicting the same sort of damage out of the same vanity, the Elly of the Middle Years onwards seems to have come to believe that love was everything she did. Every tirade, every demeaning lecture that made her children feel like crap, it came from love so it confused her that her children didn't seem happy. They must have been faking feeling terrible to make her feeling bad about loving them because children aren't smart enough to know what's good for them. This is best capsulized as Foob Facts Twenty-Two and Twenty-Three:
Fact: Elly firmly believes that her job is to teach her children to reject all the things they like because they by definition cannot know what's good for them.
Fact: Despite constantly bemoaning the fact that a childhood that she perceived as a bleak Hell-world where she was abused and trivialized because she didn't get her own way all the time has blighted her life, Elly seems to believe that nothing that happens to her children can possibly matter because of a self-serving belief in their resilience.
Since children can't know what's best for them and since children can just walk off being made to feel unloved and unappreciated because it makes life easier and since Elly thinks that having to consider how her actions might affect her kids as their being made the boss of her, it stands to reason that the reason she protests arenas and makes pious noise about how the crowd should be ashamed of itself for expecting Lizzie to fit in is the result of Foob Fact Twenty-Four:
Fact: Elly can only care about how her actions affect her personally because of that fear of being run over by her children that I mentioned.
After all, the in crowd at the junior high isn't going to say anything nasty to her if Liz doesn't wear Boston Original so Lizzie shouldn't feel like garbage. And, hey, if the kids don't like it, she can just sic John on them and get them to like it.