Are you talking about the book or the show? Because in the book, they discussed that very thing but ruled it out because of timing. They didn't know yet about the stones in America so Bree would have had to sail back to Scotland, find her way to the stones and go through. Ships don't sail in winter. By the time she got a ship and got over to Scotland, she would either be cutting it super close or it would be too late, I don't exactly remember.
So it's not like DG completely glossed over the possibility. The idea was considered and then rejected.