The problem is that Ursula was incapable of realizing why it was that her daughter hated her and never grew out of spouting rage-filled accusations that she was a vicious monster who delighted in her daughter's pain and suffering and never had any love for her or faith in her. It made no sense that someone would never grow out of the need for constant reassurance and praise and cuddling and all the other things that would surely destroy Lynn's future. Since we're dealing with a mainstay of every family (specifically, the embittered eccentric who can't and won't shut up about a perceived slight so is best left to rant because she won't change), it's clear that the more Lynn thinks about her childhood, the angrier she gets at her mother because she feels cheated because she refuses to admit that she's either somehow defective or that she's made a life and living of misunderstanding her mother.
What this means for any sort of series about a younger Elly series is that we'd have a recurring theme: a studied refusal to consider that Marian is anything other than a cruel monster who delights in inflicting pain and tearing Elly apart. The series bible and the writer would drop broadish hints that Marian is fiercely proud of and genuinely concerned for her beloved daughter but the dialogue coming out of El's lips would paint much the same picture as Deanna's please despise my mother letter. Every move the woman makes would be gratuitously misunderstood by our unsympathetic clod hero because we're dealing with someone with a fatal flaw: a hole in her soul where the ability to feel gratitude is.