If this conversation took place before she realized that she had fallen in love with the prince, Princess Ievna would have thought that the prince was just a perverted prince with all dirty thoughts in his head.
Every word he spoke was dirty, and he couldn't get rid of the perverted thoughts in his head all the time.
He simply said that he couldn't shake off the image of Princess Ievna's body, and the princess should feel offended and perhaps even disgusted by it. However, everything had changed now, and she didn't feel either of those feelings even after the prince directly whispered right in her face.
And conversely, she could feel her heart pounding after she heard the prince's words. The prince couldn't get rid of her image, and that meant she was too precious to the prince, right?