Kate thinks of consequences on the way home; choices made that change the life of those around you.
She looks at JJ and knows that this woman has made more than her fair share of these. And it's hurting her, even now. It's hurting her to remember and second guess what she might have done to avoid pain, suffering, lying...
Kate wants to say that she knows what it's like to have to lie, to keep things so close to your heart that they burn you. But she can't. Fear stops the words of dubious comfort.