you have been the one most adamant all along that this was likely a PA so I needed to come to grips with that. I did, and so this is not a deal breaker for me. Not yet.
That's a great place to be, and yes, you are right, this doesn't have to be the end of the world.
But, I will simply repeat, honest communication in which you share your genuine pain and anger in a caring, controlled way is not a bad thing. You aren't pissed at a receipt. It is the whole A and her treatment of you through it. You deserve better.
It is unhealthy to protect her from the consequences of her actions, consequences that lead to your pain and anger.
This does not mean attack her, quiz her, try to set her up and trap her in lies.
Thus, again, in whatever you say, be straightforward and compassionate to you both.