Found only in Thailand and a few areas of Burma and India, the impatiens psittacina is both rare and colorful. Its multicolored petals--red, white and blue, tinged with subtle accents and highlights--fold and swirl to form a bird-like shape. A realistic rendering would make a pretty tattoo, but your artist could add lots of fanciful touches to maximize girliness.
This endangered species of salamander has a face that could easily be made to look like a Pikachu-type anime character: big eyes, perpetual smile, broad face. Axtotls are native to two now-nonexistent lakes in Mexico--Lake Xochimilco and Lake Chalco--but they are bred in captivity by scientists interested in studying their healing powers and their ability to regenerate limbs.
If you must have a butterfly tattoo, add visual and intellectual interest by making it a gynandromorph, which is a fancy word for hermaphrodite, which is a slightly less fancy word for "male and female combined." The wings of male and female butterflies have slightly different shapes, colors and patterns. A perfect gynandromorph has one male and one female wing, which will not only make the design unique but can be a symbol of unity, or yin and yang.