Similar situation: cashier at work (now my wife) gives me cash back when I buy something; turns out two new $20s got stuck together. I didn't notice until later

Similar situation: cashier at work (now my wife) gives me cash back when I buy something; turns out two new $20s got stuck together. I didn't notice until later that night. I texted her to tell her she may have given me an extra $20 and if her drawer is short, I'll bring it back. Well she doesn't text me and gets written up for being $20 short. I bring the $20 the next day and explain the situation. The closing manager writes her up for being $20 over.