Mother in law issues

I feel like I can post this here, I'm in a mommy support group on Facebook, but a lot of the moms on the page  know my mother in law so I feel like they will blab to her. 
So my mother in law plays favorites when it comes to her grandkids. My son is the only boy and she has two granddaughters. I feel like she doesn't care about him. She never buys him anything and if she does it's girls stuff. She buys everything and anything for her granddaughters. 
We have talked to her about it and she got pissy and rude and exclude my son even more for a while, until my husband (her son) got after her and told her we refused to bring him down to see her and we would stop visiting. 
She got better after that, she still didn't buy anything for him, but still made and effort to include him in pictures and stuff like that. 
Well at his birthday party (he just turned 1) she refused to hold him and talk to him and even acknowledge him. She put all her attention on her granddaughters. It got to the point where I got snippy and refused to talk to her and hand her any cake or ice cream. I made her dish her own. I don't know what to do anymore! She just had her granddaughters over for the weekend and didn't even inform us she was getting the grand kids together for a sleep over (ps the youngest granddaughter is 8 months). I'm heartbroken knowing my little boy isn't good enough for her! What should I do? I'm at a loss!!!