Is this trauma on-going because it’s still happening, or on-going as in she hasn’t dealt with it yet? If it’s still happening and especially if it’s sexual in nature, she might need help escaping. Look into resources and ask for some professional advice from a social worker on how best to help her. If you live in a larger city in the US, 311 may be able to connect you or her with services. Librarians are also a good source for locating practical help and advice.
IRL when I’m confronted by these situations and they’re not close friends, I usually keep quiet. However reading this, I advise you to be honest with her as soon as possible. You are close friends and you have talked a little bit about trauma with each other. If you know what she is going through it may help her to know that you fully support her now that you know the extent, as long as you communicate that you found out totally by accident. In addition with how close you guys are, it would be a betrayal not to say anything to her.
Keep this to yourself. If A wanted your input, she would have asked you. I don’t mean to be harsh, but she might feel more comfortable sharing with people who’ve had similar experiences. Now, if you have had similar experiences, perhaps you could open up to A about what you went through and how you dealt with it. Then she’d have the option of disclosing to you or keeping it to herself.
Whether it’s rational or not, there’s a lot of shame around trauma and mental health issues and the last thing you want to do is embarrass A.
Unless she’s in direct danger now, I’d keep it silent. I’ve been in your shoes and I didn’t say a word for years. Everything eventually came out, in its own due time.
Thank you so much for the input guys! It really opened our eyes to outcomes that we hadn’t thought about, and I do really appreciate you guys for taking the time to comment and share your inputs. I don’t think I’ll be addressing it to her any time soon until she’s ready to bring it up herself which hurts because she’s almost like a sister to me, but I do understand that it’s a secret for her, and her alone to keep and decide to share. I’ll be deleting this post soon as I don’t feel comfortable with too much traction, but thank you so much, once again!