What's enough is his ridiculous insolence, of which the dead leaves are only a very small part. Nonetheless aggravating, though, and she opens her eyes narrowly to glare down at him, shaking the dirt off her foot back in his direction. She isn't anywhere close to shutting down so completely as to lose consciousness, but it would almost be preferable to all of this.

His question, for all its laughable stupidity, is so suddenly frustrating and infuriating that for a moment she can't even reply. Doesn't concern her? That she's trapped, blinded, useless, and at the complete mercy of the whims of a barely understood and terrifyingly unpredictable cosmic phenomenon? Without a doubt she is the most concerned of all the creatures stranded in this wretched stifling cage of a city, and he knows, he must know, how dare he.

So she isn't going to bother finding words for any of this, instead sighing bitterly. "What do you expect me to do?", she spits out, riled by her galling helplessness. If there was an obvious solution, doesn't he think she would have tried it by now? She does what the Doctor asks her to do; what else is there?