I have to jump in here. This has long been one of the narratives told by EGW/SDA’ism…the real story is something much different. The Harmon family (not her twin sister), were disfellowshipped for the following reasons, excerpted from a letter from the Chestnut Street Methodist Church…
The reason for their dismissal was not that they preached the second coming of the Lord Jesus Christ. That is a tenant of our orthodox faith which is confirmed from the Articles of Religion 1784.
Their dismissal was occasioned by their breach of discipline in proclaiming the views of William Miller’s time setting. I read these entries to mean that after much quiet counsel to refrain from their disruptive behavior in church meetings the members of Chestnut Street Church took what they believed to be their only recourse, to dismiss the Harmon Family.
You can find the complete letter here: