One, you can assume that she is being prideful, boastful, and trying to imply to others that she is better than them. I have one relative who does this same sort of stuff for these bad reasons. The best way to fight back against this is to ignore it. If this is the reason she is doing this, she is doing it for attention, and any attention (even negative attention) will make things worse.

Second, you can consider that maybe you don't know everything (shocking, I know), and consider that maybe she doesn't have bad intent in doing this. I have another relative who posts just as much of this sort of thing on social media and always makes a big to-do about her children's life events. Once, as we were talking privately, she confided in me that she had been suffering from severe depression and that her marriage was in shambles (she ended up separating from her husband, but ultimately recommitting to the relationship). To her, doing these things served a dual purpose. One, it was a coping mechanism for depression. Almost a fake it till you make it type thing. Two, during the down times in the marriage, she wanted to have bigger parties for her kids so that they could have a safe place to be kids, and they could forget about the problems their parents were having and have fun for a day.

I know you probably didn't think about the second consideration that this relative might be acting this way as a cry for help, as a coping mechanism, or out of love instead of mal-intent. Most of us don't ever think about these things that deeply. In the same way, it is possible that this affects you deeply because of your life experiences, and all of the comments that you are being petty are misplaced.

My point is, shame on all of us for judging. But then again, without petty judgmental posts, what would be left of CB?