Should I tell my gf that she wasn't traumatized?
That depends. How did you come to the conclusion that she wasn't traumatized?
She filled the criteria for PTSD and it was I who overcame her fears for her by showing her that nothing can harm her and by slowly and patiently helping her to overcome her negative thoughts.
It was kind of you to help her through this, but you really can't be the judge of how traumatized she was. If you try to diminish what she went through she will only resent you for not believing her. Just continue to support her while she recovers.
Look, I will make a decision on how to handle this situation with my girlfriend.
I understand that, but I hope you will make the decision to be sensitive and kind. Think about how you would feel to find out she is traumatized and you dismissed that. Caring for your girlfriend means treating her in a thoughtful and gentle way.