Would you have given in or stood your ground?

A customer came in to where I work today and wanted to return a painting that she bought for $350 back in February. The store I work at has a 30 day return policy so I told her that I could not return it because that was 4 months ago. She began to complain and talked about how she spends alot of money at the store and that I should just make an exception for her since she never used it. Once again I told her I could not and that it was a company policy. She begain to ague and wanted to speak to a store manager or regions. Im a assistant manager and she told me that she couldnt imagine that I got a as a manager at all because I was rude and didn’t know what I was doing (I have been working there for 3 years almost). I just want to know what anyone else would have done?