At the part of the quest line where you're sent to defuse the situation with Pacer and the NCR missionaries, they tell you to holster your weapon. Unfortunately for me, they don't initiate a dialogue box to do this, and having travel light as well as a pistol equipped and relatively light load of gear, I was basically getting shot at by the time I heard the end of the sentence since I'd been running straight forward.

Now, it wasn't hard escaping, but I'm having serious trouble trying to talk to Elizabeth Kieran. I tried holstering my weapon and wearing NCR faction armor, but she still attacks me before I can talk to her.

I'm trying to play in a way that I deal with the consequences of my actions w/out just reloading to get ideal outcomes, but this is a difficult one to just let go and shoot them all.

Did you talk to Julie Farkas before that? Cuz if you didn't then you cannot get Elizabeth to agree to peace.

But it sounds like you accidentally Elizabeth. You might have to reload an earlier save. Maybe an autosave. The quest isn't that long to reload and redo.

Edit: Clarified my post. Talking to Julie before going inside and talking to Elizabeth gets you the peace option. Neglecting to mention Julie will mean that Elizabeth and the NCR will shoot on sight.

^If the comment above mine is true, and you saved beforehand, you're fine. Just reload. Other than that, you're boned.