If you got her from a reputable breeder then she might grow some more. But my guess is, since she's merely mid sized, that you got her from a hatchery.
A jersey giant should NOT be smaller than a Brahma. That's certain.
Or, perhaps, they were obtained from a listing on Ebay or Craigslist. There's a LOT of crap out there. Jersey Giants are becoming popular and unscrupulous people are selling birds that are far below standard.Agreed. JG's grow slow, but are always big, huge body size, actual weight they put on late, at a yr though should be biggest birds in your flock.