Hey, I just thought I'd give you guys a clue on who the girl is.

5 Clues -

This is for Son-Of-Zeus : I'm afraid it's not Rachel, but not a bad guess.

She is often said to be with Nico.

She is not from Cabin 6, Cabin 4, Cabin 8 or Cabin 9.

She has a brother.

Her name has a H in it(Not necessarily a capital letter but...).

Well then, good luck...