It seems like you want closure. Which can really help in closing the book for a past relationship. Getting all the answers right, and even would help you in future relationships.
If I were you, I'd maybe call her ? Or , if you're meeting her, let her know you would like some closure and you just want to understand where it all went wrong.
I wouldn't invite her somewhere and then "bring it up" midway through conversation - chances are she won't be ready for that conversation and will lie / not give full info, or just want to leave.