Was she right to kick her Ex between his legs in this instance?

My youngest sister's boyfriend (they are both 16) cheated on her with 2 other girls from a different school, then broke up with her via text message on a Friday in September. I would have reacted heartbroken, but she was furious. She has always had a temper since she was young. When Monday came around he approached her in the hall while she was with her friends. He wanted to talk to her privately but she wouldn't go with him, so he apparently put his hands on her arm to roughly pull her aside.
She told me she pushed him away and then kicked him as hard as she could between his legs. She always wears these black heavy metal boots. He was on the floor for 30 minutes before an ambulance arrived. One of his testicles was lodged up inside of him and he needed surgery to get it out. The other one had apparently ruptured from the kick and needed to be removed. All of her friends backed up her story that she was defending herself. She was suspended for 2 weeks and is back at school now. He will be changing schools, no charges are being pressed. He and his mother wanted to keep it private. I am so thankful my sister is not in any trouble with the law.
But I am worried for my sister because she talks about the event constantly. I overheard her and her friends joking about it in the living room. They call it "popping balls". Her best friend even joked about going to the hospital to pop his remaining ball, which made me feel a little sick.
I have never kicked a boy there. I am 22 and that sort of thing didn't happen often when I was in high school but my sister talks about it like every girl does it.

Thank you for reading this far. My questions are:
1) Was she justified in kicking him? Even with those boots?
2) Would you have done the same?
3) If you kicked a boy (who you think deserved it) and later found out he lost 1 or both of his testicles, would you feel better or worse?
Was she right to kick her Ex between his legs in this instance?
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