The chicks you order are the same age as feedstore chicks...they order them and have them shipped, too. I have never had an issue with the chicks taking straight to their new mom. I have never had a hen refuse the chicks either, but then I have crazy mom centric chickens! Lol The main issue I see is being able to time the shipment right. Maybe check craigslist for someone regularly hatching and selling chicks?
That's the point. Timing the shipment and paying much more for shipped chicks wouldn't be cool if something went wrong...there are plenty of opportunities for something to go wrong. I'd say if you haven't had a bad experience then you haven't done it as much as I have
Who knows the nature of this broody hen? I've had production RIRs go broody and then kill the chicks. In her situation, a hen not properly incubating chicks is a reasonable indicator that she wouldn't be a great mother hen. Typically the best setters are the best mothers...typically.
My method would be to throw the eggs out and let her try again eventually with her own eggs.