In Madain Sari, there is a super special secret that reveals Garnet's real, birth name. You have to be on Disc 4 already and remove Garnet and Amarant from party - if you have them in your 4-person group. Go to Eiko's Kitchen and talk to Lani, she'll allude to the next room and go there right away. Press the [X] button when the exclamination mark appears. Which is this (!) symbol. Go to thw room with the pillars and the Eidolon Wall. Walk to the right, when you hear a noise go the opposite way. Go to the wall and examine each painting. Read the Ifrit painting and then a message will indicate princess Garent's Madain Sari name