Yeah, it's probably just the genetics of that particular seed.... I've got 3 plants going where 2 are "normal" size and the 3rd is 5-6" taller and always has been - opposite problem from yours but the same idea.... Your lights, obviously, are a good distance away so if she wasn't getting enough, she'd be stretching... so THAT'S not the problem. The only thing I can think of to suggest (other than just accepting her as she is) might be to add some Recharge into her feed and see if stimulating her roots would help her out. This has done wonders for some problem-children of mine at various stages and just might help yours as well. If she doesn't respond to that, I think you're going to just have to accept her!
Good luck!