I thought Group B was not sexually transmitted? I could be wrong, but as far as I know, we all have it living in our intestines and gastric area. It comes out through stool and can sometimes colonize and move into the vaginal area. I thought it was just a thing that happens randomly to some women? I don't know if I'm right though. And yes I have heard some women getting Group B after a previous pregnancy.
All women have the bacteria it just some have more than others and to much can make a baby sick when it is born. My mom had 6 kids and she only had Group B strep with one so you can have it with one pregnancy and not another.