I mean I don't know you two. I'm a 20 year old guy and I only had one real girlfriend so far. But what I've noticed is that with things like these the whole atmosphere is loaded. She is mad because of something you can't explain yourself. But she is hiding this secret from you, so you are probably a little bit angry too and also sad and devastated and worried. In return she notices this and is probably worried too. I feel like situations like these are taking a long time because both parties feel attacked.

I think in situations like these where the whole situation became so drawn-out the main problem often is not even the real problem anymore. It's the situation itself. So I don't know, maybe I'm wrong and you 2 get along with each other really well, but maybe the whole relationship is kinda tense right now. IMO in situations like these it can help to do something good for the other person. Maybe do some household chores for her, cook a nice dinner, buy her a little gift.. something that makes her happy and that kinda relaxes the whole situation. Just don't do something that might lead her to believe that you want something from her in return. For example a massage or a nice bath.

BUT like I said. I have no clue about relationships so if you follow this advice, do it on your own risk lol.