Using a throw-away, as my LTR knows my main account ID. Wondering what's the best strategy for below situation.

Girlfriend went on a trip recently with a newly single friend of hers. She got back from the trip and everything was normal for about a week. Last night she said she wanted to talk to me about something that was weird on her trip and has been bugging her. On their last night, her and her friend got really drunk and she went back to the hotel room to throw up in the washroom. Her friend brought a guy to the room and had sex with him while she was in the bathroom of the same room. Then her friend came to check on her in the bathroom and told her "we're not having sex or anything". She later went to her bed, woke her friend and the guy up and told the guy he had to leave.

Said she was embarrassed about the whole incident and didn't know how to bring it up. She said that it ruined her trip and that her friend wanted to drink and party way too much and she would never want to travel with her again. She didn't know how she got so drunk and did not plan on it (she almost never drinks). The entire time I didn't react emotionally and just said I had to digest and think about it. She started crying and hyper-ventilating and begged me not to break up with her and confessed how much she loved me, to which I just responded that she was being dramatic and to relax and stop crying. I told her that the fact that something like that happened is no big deal, I've done far worse with my friends. But I also said that the way she trickle-truthed it out over time bugged me and made me wonder if I can trust her or if I was getting the full story. If she had told me right away I probably wouldn't have had a problem with it. She's done stuff like this with me before for things she knows I would dislike or feel uncomfortable about and I told her that this has happened before and this pattern of behavior makes me wonder if this is going to be an ongoing problem. I was un-engaging afterwords and went to sleep, and she was cuddle up to me as much as possible to which I rejected.

This morning she was trying to act normally and gauge my response, to which I was unengaging again. She said she loved me before leaving to which I just responded "okay bye" and she started crying/sobbing again as she left.

I don't have any reason to doubt her story. I've always employed the 'trust but verify' strategy in our relationship and have never found anything even close to incriminating on her end. She was also raised by a good father/family to be honest and she's a huge people-pleaser that has a horrible time dealing with guilt (or a master manipulator playing 4D chess; nothing surprises me with women anymore). In regards to things that make me uncomfortable with LTRs, she doesn't have shit on the vast majority of plates or casual hook-ups I used to have. But still, AWALT stands true and you can never be 100% sure of everything.

Currently I'm going radio silent while I digest the info and figure out the right course of action. I don't intend to end things over this incident, but I want to make sure I'm not setting up a poor frame that will deteriorate things later. I want her to tell me things honestly without her worrying about me reacting poorly, which I fear may be the connection she's making in her head now as she tried being honest and it lead to me ignoring her. I think things like this might just condition her to be more secretive in the future.

I'll probably let her stew/cool off for a bit and then just address it plainly that she should not put herself in such situations in the future, but reward her for her honesty in some way so that she's conditioned to be honest in the future. If I punish her too much by withdrawing attention/affection she'll like just be secretive in the future and resent me for it.

I currently live with my LTR and we have plans to move away together, as we both hate our home city. She used to be headstrong on directing this but has fallen into my frame, choosing to go along with where I want to go and leaving when it best suits me. I should note that I have no intentions/delusions of marrying this woman (or anyone for that matter), and that I feel her behavior hasn't crossed the line in a way that would demote her. Maybe others feel differently. Would love to hear opinions.