I was a shoulder stand for my one year on the college mat, (I weigh 170 and my flyer was 100 soaking wet. :D)
The shoes can make a difference. If the shoes are sharp and have grip on the bottom, consider asking your flyer to switch them out to a nicer brand. My flyer used Kaepa's and they were way better than some of the others out there. Also, the shirt makes a difference. I wore an under armor spandex shirt underneath my t shirt or by itself, this was smoother on my skin, and when I was wearing my t shirt, the shirt slid over the spandex instead of my skin. I know most sport's bras are that spandex material, but they don't usually cover the whole shoulder. ;)
Another thing is, the more weight you can lift with your arms, the less weight that will be standing on your shoulders.
Third, try to get the flyer to a shoulder stand in one motion, if she keeps moving around, that will cause friction between your shirt and your skin, which can easily shred you.
Even after all of that, it'll still hurt, so good luck! :p