I'm a Charlotte, and people have tried to call me Lottie in the past, which I didn't like (not because I dislike it as a name, but I'm Charlotte NOT Lottie) so I would probably think it was a nickname, however if people always referred to a lo as Lottie I'm sure people would only call her that. You may just end up answering the question is that short for.....as others have pointed out.
Oh my, I hated it if anyone called me Charlie or Lottie Lol!!! They are nothing like Charlotte!!