What's Grace's secret trauma??

Maybe her sister, or a friend so close she considered her as a sister, committed suicide, by shooting herself in the head. Who knows ? Maybe she feels responsible for this person's death, thinking if she'd been there minutes ago, she wouldn't be dead, or something like that.

Yeah, the gun thing is definitely a possibility, but yes, there definitely is something traumatic! Didn't Jane point that out in an episode once?