I don't know where polygamy theories are coming from. I haven't seen any indication in Chad and Lori's exchanges that they were open to it. They seemed pretty exclusive.
Julie Rowe spoke to Emma the day Tammy died (hours later). Emma told her that her biggest fear was her father remarrying. We don't know if she had prior fears of that nature. Did Emma suspect that dad was having an affair?
I don't have any reason to think Lori would have been okay with Chad marrying an additional living earth-wife in this probation, but it was built in that she had already been Maroni's favorite wife, as well as the wife of James or Rafael or some important character from the past that was also a previous incarceration of Chad, who himself over his 30-odd experiences being a physical being of some sort on a some planet (which we contrast with being a spiritual being of some sort eternally in whatever the ether between the planets is), had wives galore- certainly more wives than incarnations.
(It cracks me up how spirits have fixed genders throughout time.)
Supposedly, Emma called Julie Rowe the day Tammy died, and said tearfully that she did not believe in polygamy. To jump to that, something had to suggest that to her for her to immediately argue about it.
My guess is Chad did say he would remarry and be sealed to another woman if Tammy's spirit left her body prematurely as he had been shown. Maybe even WHEN not if. Emma could have already been u comfortable with a polygamous "forever" family, and she could have not worried about her discomfort with it until her mother died.
That is still weird, though. Even if she decided she was not okay with polygamous forever families but put off that thought- or put it on the shelf, as I hear a lot of Mormons say, it seems like a strange thing to immediately return to it when coping with the death of Tammy.
Did Emma know about her father's affair already? I don't know. That would have made polygamy already a done deal- as it was in Chad's mind anyway- and therefore it wouldn't come crashing into relevance upon Tammy's death.
It's all so strange. It is hard to enter the mind of Emma Daybell Murray. And it is not an option to ask Julie Rowe to clear it up, either.
MIO