Instead of the SPCA, are there any Rabbit Rescue shelters around that could offer you more help? Getting a friend to adopt might be your only chance of getting her back. Have your friend go in before you release her the the shelter. Have your friend tell them what type of "pet" they are looking for (female, young bunny, black, white, etc) Hopefully, they will match your bunny with your friend "o)
Good Luck!!!
Good Luck!!!