Symbolism, Imagery, Allegory
Since she was a kid, Vera has had a deep connection to the animals at Zimmerman's Pet Shop. It's not just because she likes cats and dogs; her empathy for the animals grows once her mother leaves the family. She explains:
My first day volunteering, I took care of three Old English sheepdog puppies that had been rescued from one of those houses where crazy people have too many pets until their neighbors complain about the smell or the noise. I bathed them and brushed them and helped the visiting vet nurse apply lotion to their over-scratched flea bites. It was a feeling I can't really describe. I felt like I had purpose or something—like I was doing something bigger. (1.17.9)
Vera sees herself in the animals; she knows what it feels like to be abandoned by the people who are supposed to take care of you. By working with the animals, she is able to care for the cats and dogs in a way that her mother couldn't care for her. Perhaps this is part of what keeps Vera from hardening up completely the way Charlie does.
The animals represent innocence, they haven't done anything wrong, which is why Vera can connect to them so easily. When Charlie calls her and says that Jenny Flick is upset with him for breaking up with her and wants to burn down the pet shop, Vera isn't so much worried about Charlie's safety (since he's been a jerk to her) as she is worried about the animals. They are the innocent victims in this conflict, and she doesn't want them to get hurt. You know, the way she did when her mom up and left her.
That Vera can't save the animals when she shows up at the shop only drives the symbolic point home: Ultimately, Vera has to tend to her own wounds. She's the only one who can find the path out of the misery her mom inflicted on her by leaving—and unlike the animals, in this way, she's in a cage of her own making until she digs deep in therapy and figures out how to move on.