Hermione pushed the word "Never" to the forefront of her mind as she sensed Voldemort enter her thoughts.
She still felt sick and shaky.
She had allowed Voldemort to antagonize and incense her, her first mistake, showing too much volatile emotion, letting Voldemort provoke her. She was too overwrought to clear her mind quickly and completely. And since she was upset about Severus, those were the thoughts that were readily available to Voldemort's sly probing. She hated that Voldemort was seeing her feelings for Severus, tainting them.
But, it was better that than the information she held about Harry Potter.