This, of course, means that Marian and Elly never, ever had a substantive conversation about how Elly felt about anything. The closest either of them got was the old doll grousing about all of the things Elly did that disappointed her. Funny. The dimwitted old hen witlessly pitted Phil and Elly against each other in the name of respectability and even on her death-bed never understood why they didn't get along. Jim is no help either because he'd rather not say anything because a) he fears what people might think of him if he starts dissing the contents of an urn and b) he never had any input in their raising aside from administering the punishments his boss Marian decided on so he can't have any opinion about how Elly was raised in the here-and-now.
That being said, I can still imagine he and Phil having a conversation after the Big Sham Wedding. What'd happen is that Phil would think back to this week's arc and ask Jim what Marian would have thought of what Mike and Deanna did. Jim would allow as how Marian would have been perturbed but begrudgingly gotten behind like she did in Phil's case. When told that Elly said that Marian would surely have disowned her if she had dome something like this, Jim would be baffled. Why would Elly mention a possibility that neither he or Marian ever saw coming. The Elly he and Marian knew would have never have done so in the first place because she, for reasons they never understood, accepted sight unseen the morals and expectations of those irritating social development films they showed her in Home Ec.
The supposition would then have been that Elly had deliberately invoked an impossibility as a means not of expressing a legitimate grievance but as a means of saying that she should have final say over how he lived his life.