with regard to Clarisse, how does Mildred typify the broken relationship between herself and Montag?

Mildred doesn't seem to understand her husband's distress at Clarisse's disappearance and possible death. For Mildred, the family within her TV walls is more important than actual, living, breathing humans. This conversation comes at the point when Montag has been agonizing for days over what has happened to Clarisse, and he finally bring sup the nerve to speak about it in bed. First, he must remove the Seashell form his wife's ear; even in bed she cannot stand to be without an electronic barrier between them. Montag asks her about Clarisse and she replies:

"I meant to tell you. Forgot. Forgot."

"Tell me now. What is it?"

"I think she's gone."

"Gone?"

"Whole family moved out somewhere. But she's gone for good. I think she's dead."

"We couldn't be talking about the same girl."

"No. The same girl. McClellan. McClellan. Run over by a car. Four days ago. I'm not sure. But I think she's dead. The family moved out anyway. I don't know. But I think she's dead."

Mildred's constant repeating of information shows that one: she cannot process what Montag is asking her, and two: she is so uninterested in what actually happens in life that this conversation means little to her. She explains the death of a teenage girl as casually as she might discuss the weather, & with less emotion than she gives her "family". Thus, she cannot connect with Montag, who is beginning to question the world around him, & his role in it.