giving identity to someone else was very common way back early 90's to those who wishes to work in japan as a entertainer. I remember a close friend of mine in high school who used her sisters birth certification so she can work in japan as a singer b'coz her age wont fit the governments required age ( bit young). If thats the case of your GF it is impossible for her to get a passport again unless she would use someone elses birth certificate just like her sister. if that makes sense. No surprise your gf's family may also want a japanese man for her. I saw a lot of filipinas married to a japanese man. Most of them own the biggest houses if not mansion inside our village. Get what they want from branded clothing, bags etc. and their generosity extends to the wifes family.