Two questions: Did your mom call ahead and explain the situation? And, do you have the exact fare basis code? I don't believe I've ever seen a "non-changeable" ticket before, so I'm curious how the rules read.
That said, international travel carries with it different rules often dictated by foreign governments. For example, I believe all travel to/from India must be on fully refundable tickets, which is why flights to India are often booked well over the number of seats. Also, CO gave my brother a big headache several years back about how tariff rules prevented them from refunding a certain ticket -- they technically could have been fined by the foreign government if, during an audit, they found a violation of the rules (or so they claim). All of this is apparently in the fine print in open skies agreements, foreign government approvals, etc.
So my point is ... on an international ticket where you probably bought a really cheap fare, I think this is one of the risks of doing so.
Just curious, just how much was the original ticket?