I'm going to text my cousin to tell her that she hurt my feelings
Did your cousin say something to insult you?
Yes, and I need to vent, and to insult her in return.
Other people can sometimes be rash in their opinions, especially when texting. Take some time to cool off and think about the situation. Even if they were in the wrong, insulting them will only make it worse.
She probably would have bad vibes about me after I text her and I don't care. I just don't want her to be able to hurt me by insulting me.
It's okay for you to feel insulted by your cousin, and to want to stop her from doing it ever again.  However, if you lash out at her while you are still angry, you could just make the situation worse, and she might try to get revenge on you in return.  Distract yourself from this issue for a while, and then talk to your cousin to let her know that she hurt you.