IIRC, AS told a story of an injured ES to a cellmate, who told her family, who passed it on. I think AS said that the baby was injured, but SK said she'd be OK, so AS didn't get medical help for Elaina. Then AS claimed that she and SK discovered Elaina had died in her sleep, so wrapped the baby in a blanket and threw her body in the river.
Over time, other people came forward to add details about AS's mistreatment of Elaina, about suspected abuse of Elaina by SK. Julie King talked about kicking AS out of her house because of her abusive treatment of her daughters.
From RS's comments at the beginning of the search, it seemed to me that he implied ES had been injured.
I can't recall anyone saying that this couldn't have happened.
If you scan previous threads you'll find much more detail with references to MSM coverage.