Proxy for Tax Refund

I am a proxy for someone’s tax refund, but I don’t have the letter stating this. I have gone into the tax office to tell them that I have been designated by the person to get her tax refund and they have said they will look it up (as their computers were down that day). Is it feasible for just her name and her being on record as saying I was to receive her tax refund to be enough for this to go through or do I need to find out where the missing letter has gone before it will work?