I've wondered about that too, if that was me I would be kicking Jack's butt, as my initial reaction. But why didn't she say anything? I can understand her, she loved Ennis, had his children, lived in crappy places, only had the bare essentials, not even a washing machine, she scrub her clothes on a washboard, brilliant move convincing him to move over the laundrymat. She was married to him, and loved him. Gees after all that, you see your husband suck face with a guy outside your door. Its enough to make you go insane. It must have been like a gut-punch, your dazed and confused, your trying to catch your breath. It was something so incomprehensible for her to deal with, its like waking up and seeing a green sky.