Biting is pretty common in declawed cats. Don't really know why she's doing it in this situation, but it's probably best to discourage it before she thinks it's an acceptable way to communicate.
She may be getting frustrated that you're not picking up on something that she wants, whereas you always react when she nips. Or, she may be irritable from the heat, but you may be missing other body language cues to leave her alone. It's hard to say.