Customer gets "email error" at checkout-please help

I have a customer who contacted us yesterday regarding trouble placing an order. She said every time she hit the confirm button at step 3 of checkout, she got some kind of "email error". I went into the admin and she did place 3 orders. We use the email method of credit cards (where the first 4 and last 4 digits are in the admin and the middle section gets emailed to us). We DID NOT get the email with the credit card information and she did not get an email confirmation of any of the orders she placed (she kept trying to place the same order which is why she had duplicates).

I have gone in and placed a test order and we received the email with the CC info and I got a confirmation...as is good. However, I need to know what happened with this customer. I have not changed any of our settings since our last order was received.

https://www.thebeveragegourmet.com is the URL if someone else wants to see if they can replicate the error

I would appreciate any help to fix this problem. Thanks