I believe we all treat people in ways that we later regret. But we grow, we mature, and it's a positive thing when we are self-aware enough regret past actions.

You were at a different point in your journey back then. Forgive yourself, because you've grown and changed. You also have the option of contacting her. Maybe you don't need to say anything except, "Hi. I've been thinking about you because you've played such an important part in my life and I wanted to see how you're doing."