The problem is that being happy and not letting things bother her is not who Elly is. The woman we actually know is constantly at odds with her husband, her children and just basically the whole world. She takes herself far too seriously, is easily driven to extremes of hostile behaviour, complains so incessantly about how hard her life is and how no one can ever appreciate her sacrifices or do right by her that her husband spent the last years hidden away in his alcove to spare himself from her intemperate rages. Despite her belief that she's seen as a kind, loving, fair and firm parent her children should have turned to, she's actually seen as something of a screechy, unpleasant person.
This is not really a paradox because we're dealing with someone who's basically still a kid. A lot of the reason she and her mother didn't get along very well is that Marian sized her up and found her to be still the same irritant she used to be back in the late sixties. Elly the parent and Elly the wife exhibit the same short temper, the same tendency to take life far too seriously, the same sullen lack of interest in things that either bore or frighten her or that she isn't immediately good at, the same huffy refusal to take criticism, the same insistence that she knew what she was doing despite being pretty much an incompetent at everything, the same problem with attention, the same melodramatic insistence that no one understands or cares or will ever please her that Elly the idiot kid who cried herself sick because she was too stupid to understand what she was doing to push boys away did. It's thus best not to treat Elly as an adult but instead access her as being a small child with a small child's violent emotionality.