So far Draco had been closed off with which memories he had chosen and she had let him keep them to himself. After her gruelling work with Snape on shielding her mind, she had a newfound appreciation for the privacy of one's memories. However, if he made no more headway today, she was adamant to press him just a bit further to try and suss out why this particular memory wasn't working for him. He knew the charm and was perfectly able to cast it with enough force to blast a dozen dementors through their door, she was certain of it. He just needed the right memory.