That's a sea turtle and a jellyfish and, on the back of her calf, is this blue-ringed octopus:
She explained that the blue-ringed octopus and the jellyfish are two of the most poisonous creatures in the ocean. However, she pointed out, the sea turtle can withstand these animals dangerous venom. She transplants that fact to her own life, and pulls strength from the image of the sea turtle.
Thanks to Catherine for sharing her cool tattoos with us here on Tattoosday!