I would think at this stage she would be waddling by now and you would be able to feel the pups moving easily just by placing your hand on her belly. How big is the Mom? If she is large and has only one pup then maybe what your describing is normal.
Here's some other helpful sites.
www.homestead.com/malteseluv/whelping1.html www.hilltopanimalhospital.com/reproduction.htm www.dogbreedinfo.com/whelping.htm