Ever had to change a birth year on docs?

My Thai fiancée is 37. However, her mother (now dead) waited several years after she was born to register a birth certificate (now lost) and (because she was illiterate) wrote the wrong birth year (which makes my fiancé on paper 47). My fiance’s Gov I’d and passport say she is 47. The problem is she looks more like 27 and I expect that if we initiate the fiancé visa process, it will get derailed when she shows up for the in-person interview. I called the US State Dept and they just said to fix it before applying. My fiancé can’t be easily convinced that this is a problem since it has worked fine her whole life and her family thinks the same. Any ideas?