Hermione knew she needed to do better. She needed to at least appear to make an effort to engage, to "get better," whatever the hell that meant. She needed to allay the fears of her friends so they would stop hovering for ten bloody minutes. The problem was that effort required energy and she quite simply had none to spare. She knew what was going on, knew what she was doing (for the most part), and knew she had to keep it to herself for as long as possible. Otherwise, they'd interfere. Try to do something stupid and likely borderline suicidal. That couldn't happen and so, she determined, she had to find the energy and fake it for as long as she could. Eventually they would know. But by then... well it would be too late, wouldn't it?