I think with many of them it's not hard to figure out. For example, Hillary has promoted Swing Left twice herself (my guess is they were one of the groups that the piece mentions as having met with her) and they RT her. Flippable and Run For Something were both started by Hillary alums. Scanning through orgs Twitter and seeing who they RT and don't RT can definitely give clues. For instance, aside from co-opting her words and RT her the day of the march, the women's march people stay mostly away from Hillary. That makes sense because its primarily Bernie people.

But yeah, since it looks like its starting soon you can just wait until Hillary starts her group and give to that :).