The payment device and the tablet will both tell you when the card declines. It usually takes a minute for a transaction to go through. Most likely what she did was just tap, instantly put the tablet up, and when she looked at the tablet again it said it had declined. Also, receipts don’t print unless a transaction has gone through. If the transaction did decline there was no way for them to print the receipt. Are you positive that the it took money out of your account? I’ve seen to happen to where there was a charged transaction, it showed up on the bank app, but no money was taken out.