If an employer deposits hsa's into the wrong account, who is responsible?

I have a friend who just found out that HSA monies deposited into her account were hers and also another employees. She didn't pay attention to her bank account that much so she didn't know. Another fellow employee went to get money out of his HSA and that's how it was found out when one bank went to another (Farmers to Nextier or visa versa), this fellow's monies were going into her account. Other than the fact that yes she should have been watching her account more closely, the person in charge of benefits very curtly told her that she would be responsible for replacing the funds (in no uncertain terms)! Any ideas on this one? Thanks