brings her head down low to about waist level height, which is a little dangerous in itself. danger is part of life if she is willing to take the risk. However, I think the rulebook says that a low header (especially in tight traffic) is usually a dangerous play.

There was some knee to head contact because she brings her head down low. The defender brings her leg up a little bit into the air. The ref can't see what's happening well. Its an unusual situation when either player brings the head down low to play for the ball.

So maybe could have been a PK for BYU, maybe could have been Fryer infringing by herself committing a dangerous play that leads to free kick for OSU, or maybe the no call was right thing. Its occuring right in the mid-region so halfway between (A) obvious heading area when ball is near head/shoulder level and (B) ball being on ground level. The ref probably couldn't see whether or not there was knee to head contact anyways.