Can I tell my friend that the only reason her twitch is more successful is because she is a girl?
For what reason would you tell her such a thing as it is a gender issue with popularity on Twitch?
I want to get back at her for stealing my boyfriend
Getting jealous of another girl is your downfall, but you are also a girl. Be more mature about it and just forget it. Jealousy makes you look pretty pathetic and you don't want to have a reputation for it.
She's ruining my life, I can't let it go. I will get her, even if I have to ruin my life too.
You shouldn't be jealous of a friend, and while what she did to you was messed up, the best way to get back at her would be to find a better boyfriend or improve your life in some other way. Lowering yourself to attacking her will just make things so much more complicated for you in the long run.