Why do women tear each other down

My so called "sister in law " said to my husband that his with a useless woman(being me) who can't even given him kids.

My heart broke into a million pieces. I cried like a small child. My husband was so infuriated

Might I add hubby and I have only been trying for 6 months.

And she (SIL) struggled for 3 years and had medical assistance to fall pregnant . Not once have I ever been rude or nasty to her. And she throws a comment like that at me.

She could have personal experience and knowledge knowing how that statement can hurt someone, especially since she knows a baby is all I can think about.

I'm just hurt