Later, she makes fun of Harry by talking "baby talk" to him. But, in The Half-Blood Prince, she has the following dialog with Severus Snape:
"You ask why I did not attempt to find him when he vanished. For the same reason that Avery, Yaxley, the Carrows, Greyback, Lucius" — he inclined his head slightly to Narcissa — "and many others did not attempt to find him. I believed him finished. I am not proud of it, I was wrong, but there it is.... If he had not forgiven we who lost faith at the time, he would have very few followers left."
"He'd have me!" said Bellatrix passionately. "I, who spent many years in Azkaban for him!"
"Yes, indeed, most admirable," said Snape in a bored voice. "Of course, you weren't a lot of use to him in prison, but the gesture was undoubtedely fine —"
"Gesture!" she shrieked; in her fury she looked slightlly mad. "While I endured the dementors, you remained at Hogwarts, comfortably playing Dumbledore's pet!"
"Not quite," said Snape calmly. "He wouldn't give me the Defense Against the Dark Arts job, you know. Seemed to think it might, ah, bring about a relapse ... tempt me into my old ways."
"This was your sacrifice for the Dark Lord, not to teach your favorite subject?" she jeered. "Why did you stay there all that time, Snape? Still spying on Dumbledore for a master you believed dead?"
"Hardly," said Snape, "although the Dark Lord is pleased that I never deserted my post: I had sixteen years of information on Dumbledore to give him when he returned, a rather more useful welcome-back present than endless reminiscences of how unpleasant Azkaban is...."
"But you stayed —"
"Yes, Bellatrix, I stayed," said Snape, betraying a hint of impatience for the first time. "I had a comfortable job that I preferred to a stint in Azkaban. They were rounding up the Death Eaters, you know. Dumbledore's protection kept me out of jail; it was most convenient and I used it. I repeat: The Dark Lord does not complain that I stayed, so I do not see why you do."