Hepatitis B, like hep C, can be transmitted through a vast array of exchanges. Sexual intercourse is thought to be a relatively rare cause of acquiring hepatitis B. The most common ways it is acquired are: being born to a mother who has the disease, receiving blood transfusions containing infected blood, sharing dirty needles especially in the context of illicit drug abuse and acquiring the virus in a hospital. Even once all these causes, as well as the possibility of sexual transmission, have been excluded, 15% of people with the disease will never find out how they acquired the disease. Vaccination for your girlfriend most certainly is an option you must discuss with your physician; I would recommend the careful use of barrier contraception before such a time, perhaps refrain from intercourse until them altogether.