I just found out my ex-girlfriend is cutting herself again
How did you find out she is cutting herself?
I saw her arm that had visible scars
It is good that you noticed that she is cutting herself. You should try and get her help before she really hurts herself.
Nah, I would rather tell other people online about it.
Something is obviously wrong with her and she is crying out for help. Even if she gets offended you should try to get her in therapy or someone she can talk to about her stress and frustrations.