...read it through looking increasingly incredulous.
Ginny asked Ron incredulously.
Ron turned to stare incredulously at Harry as his mother hoisted the laundry basket and the teetering clock into her arms and stormed out of the room.
Then he saw Harry’s, and a look of incredulous delight spread over his face.
Scrimgeour turned slowly on the spot and exchanged an incredulous look with Fudge, who really did manage a smile this time as he said kindly, "The trouble is, the other side can do magic too, Prime Minister."
"Not of great importance?" repeated Harry incredulously.
’What d’you mean, you don’t care … don’t you want to leam to Apparate?’ said Ron incredulously.
"What for?" demanded Ron incredulously.
"And Dumbledore believed that?" said Lupin incredulously.
"Rosmerta?" said Professor McGonagall incredulously, but before she could go on, there was a knock on the door behind them and Professors Sprout, Flitwick, and Slughorn traipsed into the room, followed by Hagrid, who was still weeping copiously, his huge frame trembling with grief.
There are no more uses of "incredulous" in the book.
Show samples from other sources
I find it incredulous that you believe she is sincere.