Please help - I'm trying to buy a female bird for my daughter's birthday tomorrow

wacko

and I have found one through a breeder that is a whiteface pearl pied. I have been told that because only the father carries the pearl gene it is definitely female.
I have been trying to figure out cockatiel genetics but I'm stumped on the whole matter. I'm hoping someone here has a better handle on the sex-linked genes... and can let me know if I should go ahead and buy this bird!
Thanks VERY much!