Cost price disappearing?!

Hi, I've just been with a customer who swears that cost prices she entered when creating a new item had vanished when she went to print labels next day. It sounds totally bizarre to me and as I wasn't there when she was creating the items, I can't say for sure that she did indeed enter the cost price, which would be my first thought. As she's not new to this I really can't turn around and call her a liar! I figure all I can do is ask and see if anyone else has seen this happen, though I'm not hopeful! She's demanding answers, thinks the system is corrupt and I'm not sure how I can approach this and politely say "user error". Thanks.