You only transmit genes to the baby at conception. Genetics is not how Hep B is transmitted. The mother transmits genes and, since she carries the baby in her body for nine months, all bodily fluids to include blood and nutrients and everything else go to the baby, so since she does not have Hep B, no, it won't get transmitted. Unless YOU are giving birth to the baby, the baby will not get Hep B. To be on the safe side, the mother should reveal to the delivery physician or her Ob-Gyn that you have Hep B, that way they can test her for it to make really sure she hasn't gotten it in recent months, and will be able to treat the baby appropriately when born.
Why not ask her obstetrician?