You can create the scene with a plywood, and sticking up artificial grass.
You can put the doll in the posture that you want with wire. You can put it inside the doll even, before finishing sewing it, so that the wire is not visible. And if you need to, stick part of the doll to the plywood (feet for example).
id sugesst plywood and mounting the doll on that or if u wanted to crochet the whole flowers grass ect u could do the whole thing and then use cardboard as a base and wire to make the doll stand ect to make her movable?