Its how the old building society accounts worked. I used to look after setting up BACS payments to pensioners for a life assurance company, and getting the old dears who wanted us to pay them into their building society accounts to give us all three numbers was a right pain in the wotsit. If...
Hmm, Nationwide... I could see there being a problem if this is one of those 'accounts' where a block of customers have the same sort code and account number, with each customer having their own reference number. She gets the account number right, so the money gets into the pot (the account)...