May be the easiest way is for gf to check her blood to make sure whether she has immunity againt hbv. Some people who were priorly vaccinated may lose or diminish their immunity against hbv with the passing years. In that case they should take a booster vaccine.
Depending on what year. My kids all needed to get into day care and school. How old is your gf. Best thing for her is get tested and then get vaccinated. Even if you guys don't end up getting married or stay together forever, at least she will be protected for at least 15-20+ years. It's best for health also. If she has insurance, it will cost almost nothing