The One and Only Bob by Katherine Applegate

Disclaimer:  I have not read The One and Only Ivan. :)

Bob is a little Chihuahua mix dog who lived with Ivan in the roadside show. He has now been adopted into a loving home, Ivan is in a local zoo being well taken care of, and Ruby is there as well in the enclosure next to Ivan.  As the story starts Bob goes to the zoo with his people and is talking to Ivan.  There is supposed to be bad weather later in the day, but all of a sudden all the animals are told to go to their enclosures, his people are getting inside, and Bob falls over the wall into the gorilla enclosure.  He is picked up by a tornado that shoots him across the park and he ends up in the giraffe enclosure.  As he makes his way back to check on Ivan, Ruby and his people he encounters danger, difficulty, and a surprise that ends up helping him get over his guilt over his siblings.