Hi,
I am a great niece of Aunt Rebecca. Her sister was Kate Knabenhoff, my great grandmother, who married a Berman.
The Bermans had 3 children one of whom was Charolotte Berman who married a Kalotkin.
My grandmother was Charolote (Berman) Kalotkin and my grandfather was Julian Kalotkin.
From doing a search here it appears that Rebecca's father was Philip Knabenhoff. His father was Elias Knabenhoff.
The Knabenhoff origin as per this site was Smergon, Russia, Lithuania.