No it's not a new phenomenon, I have known women in the past who were disappointed with the sex of their children, but of them all, only one went on to be pretty unfair to her daughter. I was so angry with her one day, when she said that she preferred her (younger) son to her daughter and had only ever wanted boys. I said 'I hope you have never let on how you feel to her' (the child was nine at the time) and she replied, 'Of course I have'! I'm afraid I couldn't ever speak to her again.
This was because my own mother had always wanted a boy, and had four girls and lost one boy. We all felt unworthy. I asked her about ten years ago why she had hoped that we would all be boys, and she replied in amazement that she loved us all being girls, but knew that our father would have loved a son. Maybe it would be worth asking why she feels like she does. Also, maybe it's her hormones making her more upset about it than she would be normally. It's so sad, I do hope she manages to get over it.