I think Disney princesses will always have a soft place in most of our adult hearts. When we were young, they were the cartoon women we idolized, sang along to, dressed up as on Halloween (or just a Monday), and who we sometimes dreamed of growing up to be. As an adult, you can't really dress up as them any more per se, unless its really for like a Comic Con, or a Halloween, or costume party, but you can "adult" your favorite characters by bringing in elements of their costumes into your everyday wardrobe.
She was one with nature, and knew every rock, and river, and tree, and creature had a name. Incorporate pieces in more natural colors (ahem, of the wind) and fabrics, but honor her love of animals by making sure your pieces are only faux. You can pay homage to her tattoo by showing off your own in a one shoulder top or getting the temporary kind. To bring her signature dress into the modern age, find something earthy, a little fringy, with a bit of movement to it, and top it with a large turquoise neck piece or necklace. Keep your accessories minimal and simple and a reflection of all things natural.
Small town girl with big dreams in New Orleans ends up living the swamp life after one fateful kiss. Use your outfit to pay homage to the lily pads found in the swamps and bayous wearing floaty chiffon tops and dresses with flirty details. Look for items with flowers, like a floral necklace or headband, or a pattern to go on your handbag with a floral motif. You can even find details like a ruffle, flower, or pleating in a shoe to bring the theme together. Stick with all manner of greens and yellows and browns. You can also mimic her costume party princess dress by wearing a blue dress with a bit of sparkle.
Also a lover of animals and creatures, she is the fairest of them all much to the chagrin of her evil step mother who sends a huntsman to kill her off. Jealous much? You kind of have to rock the headband with the bow in it for sure. Bring in tiny details that highlight her love of both the seven dwarfs and all the creatures by wearing a charm bracelet with seven unique charms on it, or rocking a necklace, or bag with some type of animal on it. Bring in her signature colors with a combo of red, blue, yellow, and white with a cute pair of skinny jeans, or a strapless top, or embrace the bad, with a bit of plaid and some combat boots (nod to the huntsman).
Young mermaid dreams of becoming a human, but be careful of what you wish for. Her three signature colors are purple, green, and red. Your accessories can be a subtle nods to the ocean like a sea shell necklace or earrings of purse. She loved whatsits, so be as quirky as you'd like without going too overboard. Match up a rich purple with the the turquoise color of the ocean, and match up with various colors of green in a shoe or tailored jacket. If you don't have the red hair yourself, you can tie it in in a shoe with a few whatsits dangling about, or a clutch.
The princess must marry, but only wants to do so if she can follow her own heart and marry for love. It's the summer, you can definitely rock a crop top like Jasmine in her signature color which works well with a few gold bangles or a statement gold necklace and earrings. Pay homage to her pet tiger Rajah, in some tiger frame sunglasses, or tiger print bag. Wear a gold sandal, heel, or flat and let your hair way down.
She is a young woman who goes rogue chopping off her hair and dressing as a man in order to defend her fathers and her family's honor in battle, so that he, injured, wouldn't have to. You can play with the dichotomy of the character in your outfits. Go tomboy with one look imitating her war gear mixing and matching the feminine with the masculine and on the other end, showing off societies expectations of her in her more feminine style of dress in a mix of bold yellows, blues, and greens.