seriously though, here hands hurt her when she's on the OLD bike - so everyone is to make assumptions (including the sales guy at the bike shop) about her old bike and her position on that bike as well as how she ends up on that bike after riding for 15+ minutes... ???

If you wanna be big bro (or little bro), then I would call the shop in question, speak with the mgr about your concerns. Give Sis the mgr's name and if she goes to him, he'll likely know how best to proceed. And if you want to be more 'thorough', convince your Sis to bring her old bike along for comparison... A quick flip of bikes in the parking lot will at least give her some confidence that the new bike starts out moe betta...