God can't be a woman, any more than he is a man, he is GOD!
EDIT: Don't take my "can't" to be limiting towards God, I realize he is omnipotent. What I mean is that given the context of th Bible, God can't be a woman. And yes, I realize that Jesus the Son became man on earth, but I was referring to the Father.
We refer to him with male pronouns because Jesus instructed us to pray in that manner and referred to him as Father.
Matthew 6:9-13 (New International Version)
9"This, then, is how you should pray:
" 'Our Father
hallowed be your name,
10your kingdom come,
your will be done
on earth as it is in heaven.
11Give us today our daily bread.
12Forgive us our debts,
as we also have forgiven our debtors.
13And lead us not into temptation,
but deliver us from the evil one.[a