she barely had the energy to stomp on the spider, let alone the will strong enough to care.
Could you please tell me what the object of "care" is?
Also, I don't know it means "she could not care about herself" or "she could not care about the spider".
The fuller text is here:
A scuffling sound caught her attention. She saw a tarantula, body as big as an apple, scurrying out from its hiding place in the corner. She got to her feet and used the mop to chase it outside. It was crueler to send the spider back out into the heat than to crush it with her shoe. Besides, she barely had the energy to stomp on the spider, let alone the will strong enough to care. She had trouble lately doing anything that didn’t result in food or water. The key to life in this dry heat was conservation of everything: water, food, emotion. That last one was the biggest challenge.
The Four Winds by Kristin Hannah