There may be just a difference of emphasis here. An enlightened person wouldn't be constantly horrified to the point of insanity. She'd be at peace with the universe, but the question is about the exact character of that tranquility.
If nirvana is the absence of character, I don't think it would reflect nature's universal flow. Granted, that flow is mindless, so enlightened inner peace would be likewise mindless (neither selfish nor bleeding-heart selfless).
But there is a character of physical law, evolution, and complexification. Nature is creative and destructive and alien to the human mindset. Fitting that alienness or inhumanity into a human form shouldn't produce mere blase acceptance. It's the vacuity of standard mystical tranquility that misses the mark for me.
The enlightened person's inner peace should be touched with grimness and Nietzschean madness as well as horror, disgust, sorrow, and awe. Rather than being governed by these reactions, she'd be at peace, but she'd be a human person that reflects the reality of inhuman nature.