I think most of the women who post in this forum completely understand that being sad not to get your girl doesn't mean you will not love your boy.
Abso-fragging-lutely! It takes time, and yes your mother does have a point, but right now it hurts, really hurts and you are absolutely entitled to feel that way, and be upset about it. You know you will love this boy, but there is nothing wrong whatsoever in taking some time to grieve for the daughter that you will never have. I wish I could fix your pain, I really hope you feel better soon x