This is because it's clear as anything that Marian Richards and Thelma Baird would have taken an instant dislike to one another. Next door to Elly is a professional dog breeder who saw pets as a positive thing that enriched lives and who didn't see the point of Elly's regime of endless screaming and never allowing herself to be pleased by anything. Back 'home' on the West Coast is a bitter lunatic who hates dogs because of her own lousy childhood, kept Elly from winning arguments to make her a nice child and who thinks that if a child is allowed to know that what she does pleases her mother, said child will simply sit down and die in a puddle of her own filth because an idiot English Canadian like Marian is hard-wired to imagine a child thinking 'My mommy loves me so I don't have to exert myself or grow or get better; I can now just vegetate because I'm loved'.
The irritating thing is not just that Marian would clearly have thought she won the inevitable argument about her lousy methods and how they made Elly the paranoid bug-fuck crazy rage goblin she is today because fate denied Thelma a child. The irritating thing is not that Marian never regretted a single hurtful word or shrugged off her child's heartache. The irritating thing is, as always, that Marian is too damned stupid to understand that Elly isn't a normal person. She died never understanding that Elly took her to mean only what she said she meant and went to her death not accepting the anecdotal evidence of husbands, sons, sons-in-law, relatives and others who didn't know what they were talking about that suggested that Elly saw herself as a despised and regretted disappointment who couldn't make her mother happy, Elly God-damned knew that she was loved and respected and no one had to tell her that.
Ah, well. Since this strip allows for a sort of bullshit afterlife with ghost dogs hanging around trees so they can play with their abusers and dead women sewing Miracle Dresses, we can imagine that instead of Masky McDeath ushering her into the void, Thelma would be there to show Marian the truth. Since, as the Japanese say, only death can cure a fool, only death could make Marian see the damage she did loving Elly in a way she couldn't understand and that made her feel like a garbage person. This is why I think that instead of Marian's ghost helping out with the dress, that's Thelma subbing for someone who avoids her family out of shame.