<human>: I come from a very big family, and we're all relatively close. One of my cousins has had a lot of issues with school and health, but is also a very judgemental human being. She constantly mocks people we went to high school with, her immediate family, and our cousins. At first I could write it off as the same teen angst I had, but now I feel as if it's gotten out of control.

A few months ago, I guess she made a humorous Instagram account so she could section off funny posts from her "glamour shots" so to speak. I did not follow it back because I knew it'd open a whole new can of worms. However I checked it today out of curiosity and was not happy with what I found. She posted something mocking my cousin's old Instagram. Keep in mind this cousin was 11 at the time she wrote this. Currently the cousin under attack is an amazing 14 year old girl who would never do something like this. I am afraid to speak up about this because I know I may be the next target. I deal with enough people from college judging and bullying me at the moment and I don't think I could take one more person hurling insults at me behind my back.

I'm at a loss as to what to do. Should I tell the mother of the young cousin who's being mocked? Am I overreacting? Keep in mind I've seen this kind of relentless mockery go on before my eyes for years... I know it's wrong but now I want to do something about it once and for all.

Can you succinctly summarize the text in 1-3 sentences?
<bot>: My cousin has been incredibly mean and judgemental about our family behind their backs for years and I'm done being a silent witness. I have proof of her meanness and I'm wondering if I should go through with telling someone.