Board Thread:News and Announcements/@comment-69.171.163.204-20140211230902/@comment-24891101-20140523191740

Or, there could just be different naming conventions in Remnant. Or, Ruby could have had her name legally changed to Rose, to give her closer kinship with her mother (assumed to be Summer Rose), since she was quite devastated over her loss, however that may have happened (see Red Like Roses II and Gold).

I'm also still on the half-sisters idea, myself, though.