Did She Try It On Purpose?

Last night me and my friend went to toysrus in durham nc to buy some gifts/toys and to make a long story short when i got to the checkout my bill came up to $81 luckily i had already scanned the items beforehand so i knew it couldnt be right, well what she/checkout girl did was scanned 1 item that cost $21 twice so in reality my bill should've been $61 i confronted her about it and she gave me back a refund. She did'nt seem very surprised. But do you think she knew what she was doing/meant to cheat me?