Without knowing how old the kitten is and whether its been fixed or not, I will have to agree with you. I say girl too. :-)
Almsot 4 months and not fixed
At four months it seems like the little ballsies would be budding. I say girl too. Don't be too tough on your friend, it can be pretty hard to tell with young kittens -- females can get these little walrus-mustache looking things on either side of their top of their vagina that look like nascent testicles.