Some BPs will eat, some won't while in shed. Personally I don't even offer if any of my balls are in blue on their feeding day: they usually don't take it for me (I feed f/t).

If you do offer and she doesn't eat, I'm sure the pet store would take it back (I would call though beforehand) or you could keep it until next feeding (if you have a mouse/rat setup) or simply prekill it and freeze it if you think your snake will eat f/t her next feeding. Or feed it to another snake if you have any others.

If she eats it won't affect her shedding: it never does when my other snakes eat while in blue. Just keep your humidity up.