Corrected entry: Mavis knows her parents met in Hawaii because she found her father's souvenir postcard. Mavis is 118, which means her parents met in the 1890's at the latest. There were no postcards like that for Hawaii in the 1890's.
Phixius
23rd Oct 2013
Correction: There's no reason to think this. The US was first introduced to postcards in 1873 (although they were invented in 1840) and the first "souvenir" postcards were sold in 1893 (before Mavis was born). By 1898, over 200 companies were selling Hawaii postcards, so obviously there was a market for them and no reason to think local businesses couldn't create said postcard.
Bishop73