All my first eggs are small. Most of the first few months' worth are pretty little. Then, once in awhile, those newbies will blow you away with a monster egg.
How big they will get depends on the breed, but the first ones will generally be little.
If it is the BA I would say the egg will get bigger, but when I have not a clue. Winter has been slowing egg production all over, but not everybody. I would defiantly give her till spring.
My girls first eggs were all tiny with yolks the size of marbles. They have gotten bigger. I always know when someone lays a first egg. I have confirmation that 4 of my 5 pullets are laying. Not sure who is holding out exactly but I think I have had 5 tiny eggs in the last three weeks.