Clara blinked at the Doctor's reaction to her predicament. She glanced down, already knowing full well her state of undress, but when he said it, she felt it warranted at least a glance.
She looked back up at him expectantly, with wide eyes. He wasn't getting it, was he? She stayed looking at him like that even when he put his big hands on her cheeks. Patience was a virtue in this house, well with the Doctor at least. He would get it, eventually, right?
"Unless I'm missing something?" BINGO! There it was. Clara nodded her head in affirmation, her eyes lightening from their expectant look to a relieved look.
"Yes. Yes, there is something you're missing. I changed back against my will," she said evenly, though a sense of panic was starting to set in. The Doctor hadn't looked like he was in the middle of an experiment when she walked in, so the chances of him causing this was significantly dropping. Then another realization hit: she couldn't shift into anything, either.
Her eyes grew big at this thought. "Oh no, I can't shift either! Watch!" She directed, moving away from him to attempt to shift. Clara relaxed her body and pictured her chocolate cat form. By this time, she was normally shifted by now, but she looked at her still human body and knew she lost her ability.
Looking back up at the Doctor, tears started to crystallize her eyes. Clara declared, "I've lost my powers."