Answer

I didn't understand what there is in the Ran on this issue.
Are you asking which of the two olives is nullified according to the side that it cuts it off entirely? Apparently that really is an ontic doubt. Therefore, when she ate one of those olives, according to the side that it cuts it off entirely she is in doubt about a prohibition (an ontic doubt). And its doubt is treated stringently even if this is a rabbinic vow. This is no different from partnership and all the other cases of selection I described.
As a matter of Jewish law, we rule that it merely weakens it, so there is no practical legal difference here.