What should I do?

So, my husband and I have 2 boys. My MIL has her favorite which is our older boy. She really doesn't have much to do with our younger son, like at all. She will send him gifts at Christmas and birthday like our older son but if she gets on video chat or phone call she never asks to talk to him or see him. This has been an ongoing problem. My husband and his mom don't really talk because they had a falling out and that's a story for a different day... anyways, she put up a post on Facebook last night while I was at work talking about she videoed with my older son and he's amazing and she misses him and he's the best etc., and in some of her screenshots I could see my younger son next to his dad in them and she said nothing about him. At all. I'm hot about it and I want to text her but I want some input first. Thanks ladies.