Man, that is f*cked up. That is NEED TO KNOW INFORMATION.
Here is the lowdown:
Hep A is transmitted via ingestion of fecal matter, even in microscopic amounts.
Hep B is transmitted via contact with infectious blood, semen, and other body fluids from having sex with an infected person, sharing contaminated needles to inject drugs, or from an infected mother to her newborn.
Hep C is transmitted via contact with the blood of an infected person, primarily through sharing contaminated needles to inject drugs.
Hep D is transmitted via contact with infectious blood, similar to how HBV is spread.
Hep E is transmitted via ingestion of fecal matter, like Hep A.
I suspect it's probably C, which is why she hasn't told you. Treatment is not always necessary with Hep C, but keep in mind this is a virus, not a bacterium.
I think you should file suit for intentional omission of her communicable disease status. That is a serious crime.