The problem is that it means someone else received the bag she ordered and got charged for the one she got, it's a lot of hassle for the person who received a bag worth less.
However,
If the store don't call you then it's your prerogative to keep the item. An exchange has been made and people are being paid to send out the correct orders.
By law you are well within your rights to keep the item and not pay the extra, the store would have to (to make up the funds).
I'd say keep the bag and wait for a call, if she calls them it'll be so much useless hassle when they probably haven't even noticed.
However,
If the store don't call you then it's your prerogative to keep the item. An exchange has been made and people are being paid to send out the correct orders.
By law you are well within your rights to keep the item and not pay the extra, the store would have to (to make up the funds).
I'd say keep the bag and wait for a call, if she calls them it'll be so much useless hassle when they probably haven't even noticed.