In the burn ward, it isn't the dying woman that upsets her. She knew it would be horrifying, and she is there to do a job. She takes her lead from Hotch's quiet, comforting voice, the softness in it surprising her, and as she listens to him she realises this job will not be what she thought. She expected clear cut, truthful, no more outright lies to material witnesses.
It was naïve, and letting it go feels like losing another part of herself. But respect for him expands in her chest, and she realises he isn't what she expected either.