one of the things about long arm quilting---which should be discussed with you before you piece your backing-is
if there is one seam on your backing it should be horizontal---not vertical-
when it is horizontal (which is probably why she loaded it sideways) the seam lays nice and flat across one of the bars- turns evenly keeps everything nice and straight
if the seam is vertical with each turn of the roller right in the center you get 4 layers of fabric---building-building building--when its small (only a few turns not too big a deal- if its a large quilt by the time it is rolled up the center where those layers are growing can be 10" thick- with 40 times less fabric on the outside edges...causing baggy sides- which can be quite difficult to keep from puckering-causing problems-
when someone brings me a quilt with a back seamed vertically i do explain and show them the problem- and we discuss how it will be dealt with- when possible i do turn them- if the design will not allow turning---sometimes they have to take the back and start over- sometimes we deal with it---but i ALWAYS tell a new customer before i get that first quilt how their backing should be pieced.