Because of the Rabbit, by Cynthia Lord (author of Rules) is a charming story about a girl who finds a pet rabbit the night before she starts going to public school for the first time. Up until this point, Emma was homeschooled. She worries about being different and not making friends.
Drama happens, both with Emma's attempts to make friends at school and with the bunny. What Emma is going through feels very universal, as is the message that to make a friend, you have to be a friend.
At 183 pages, this is a quick, fun read, and you might learn a little about rabbits.