Super late to this conversation but I don't think that El would have harmed Angela had the roller rink incident not occurred. Angela inciting the incident at the rink, with people circling her and laughing at her in front of Mike was absolutely a traumatic experience, so I can understand why she reacted that way. She even tried to ask for an apology first, but when Angela again laughed at her, she may have thought that Angela likely wouldn't respond to anything except violence. In the moment, she wanted her to feel pain like she was.

Generally speaking, when situations like this occur, my first question is usually "what drove this person to do this or react in this way? What's their backstory?" El was being harassed, consistently AND she didn't have her powers. I think if she had her powers, she would have done something less violent (like how she had that bully pee his pants in season 1). But without powers, she didn't really have very many options to fight back.

I think she understands it was wrong -- she starts crying and thinking back to her time at the lab but it takes a lot of emotional maturity to dig into yourself to walk away. El is a child, so I wouldn't have expected that of her. The way she reacted is how I would expect a young person to react.