When you call to report your card lost/stolen, the bank will immediately suspend the card. It may still be possible to call them back, tell them you've found the old one and have them activate it again.
The first step is figuring out where she gets the phone. Does she get an allowance and use that money? Stop her allowance. Her friends? Limit interaction with those friends....
No, the barcode is for retailer use only. Contact Microsoft and give them the card information (typically the barcode number above the barcode and/or the remaining 12 letters).
Yes. It would be best to either call your bank's customer service number or go into a location and tell them you lost your card. They will probably need your...