While most people naturally write from left to right, lefties do the opposite at first -- they move from right to left. The same goes for drawing circles: Righties do it counterclockwise and lefties clockwise, which is why they tend to reverse letters (like a, c, d, f, g, q, and s) that are made with a counterclockwise stroke.
To help her adjust:
Teach her to hold her pencil between her thumb and forefinger, resting on her middle finger, at a 45-degree angle -- except that it should point toward her left shoulder, not her right.
Buy her pencils, notebooks, and other supplies designed for lefties. Soft, molded pencil grips with an "L" marked where her thumb should go will teach her the right grip.
Slightly raise the left corner of the paper she's writing on to keep her wrist from curving, and her muscles from straining.
Help her orient herself from left to right by drawing a thick green (for "go") line down the left-hand side of her paper. Tell your child to move away from the green line to the right.
If your child is sitting in a group or next to a rightie, have her sit on the left, so she doesn't bump elbows with her neighbor.
Most lefties make smudges as their fist moves across the page. Let her know that's okay! What's important is that she gets the basics down.