Some kids are simply extra-sensitive to new textures. Try bringing some natural objects inside and letting your child examine them in familiar surroundings, where they won't seem quite so overwhelming to her. Hand her just a single daisy, some blades of grass, or even a budding twig.
Outside, don't push her to run wild if she doesn't want to: "Spread out a blanket, sit on it with her, and let her extend a hand or foot onto the grass at her own pace," suggests Rebecca "Kiki" Weingarten, an education and parenting coach in New York City. Soon enough, nature will feel like, well, second nature to her.