Re: A New Girl
I suspect your comment that the arm is going to be a challenge means that you were originally thinking of a one piece mould over the top of here with the opening where her shoulders and rear end meets the base. If so then I think your easiest option would be to cut arm off and mould seperately.
My personal choice would be to make a multipart mould, one main piece for the top and two smaller pieces for the under arm and behind the back.
Keep us updated on how you proceed