Should I apologise to a girl I was mean to 4 years ago?

So I'm really ashamed of this, but I was mean to this girl at college who I lived with. I basically started drama out of nowhere, I was immature and I would start random arguments out of nowhere with her when she didn't do anything wrong. Two guys in my group of "friends" at the time (we were all not very nice people) started making fun of her as well and I did nothing to stop it. This girl ended up moving colleges because of how people treated her. We were all basically bullies.

It makes me cry thinking about how I acted back then and how horrible I was. I am deeply ashamed of myself and am trying to atone for what I did. I was thinking of sending her a message telling her how sorry I am and that she didn't deserve any of it.

Should I apologise to her or would that be selfish of me to do? I don't want to re-traumatise her but at the same time I really feel she deserves an apology. Or should I just leave it be and learn from it?

Should I apologise to a girl I was mean to 4 years ago?
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