This is because we're being beaten over the head with why it is everyone hates this woman: she thinks that she's doing them a favour and it's one they don't want. She honestly seems to believe that to have a good marriage, one MUST start with a lovely wedding ceremony and Deanna values what she sees as simplicity. It doesn't and can't occur to Deanna that her mother feels cheated out of something because what makes her fit in so well with the Pattersons is her refusal to meet someone half-way.
Another favour that Deanna rejected was spending the first years of her children's lives with them. Deanna spun is saying "I don't want to end up resenting my children" but, as it was with Elly, it meant something like "I don't want my children to figure out that I resent the time they take out of my life." Mira's fondness for children and belief that time spent as the 'slave' Elly doesn't want to be is not wasted is seen as a bad thing because it forces a moron to realize that she's too squishy inside to deal with the emotional needs of her children. Deanna thinks that it's the job of everyone who isn't her to tend to her children but much like Elly expects unearned fealty; this means that she cannot dispense respect that is actually earned. Since the Pattersons have the same destructive belief, Mira gets demonized for doing stuff most people would respect.
What really makes this all distressing and loathsome is that Deanna can't wait to slobber about how supportive and wonderful Elly is when it's John who knuckles under and lets Mike steal the house and it's usually someone who isn't Elly who actually watches the children she wishes were dolls she could put away when she gets tired. She doesn't even get the warm steam off of Elly's pee but Elly is the best person ever because she doesn't "intrude" or say confusing, hurtful words that prove that she has no faith in Deanna like "Why should our new baby have old things?"