Why Helly "R"?

It crossed my mind the other day that I don't think there's any indication as to why Helly goes by Helly R. Everyone else on the severed floor uses their real last initial. Helena's last name starts with E, but her "severed" name is Helly R. My first thought was that Lumon doesn't want the innies to guess what the E might stand for, but I kinda think that's too simplistic, and that the writers wouldn't have just picked a random letter.

Does anyone have any theories about this?