In the best scenario she should have calmly explained it, but with something like that its understandable that she would snap at her roommate. Grieving like that, especially at the beginning puts people on a short fuse and everyone takes death differently. I can also see the roomate making that mistake, I dont take anyones death I haven't really seen in the last few years seriously. I would've taken your girlfriends side more, but with empathy for her roommate. Maybe just sat on the fence and explained it to her roommate for her and let her roommate deal with it rather than being stuck in the middle. I'd say still NTA because you did what you could in the moment. Both your gf and her roommate were wrong in a way.