I think it's actually easier to teach lateral moves on the ground than in the saddle.
First, does your horse already know how to side step? You need to teach her how to move laterally in general before you can start adding forward motion. You can teach her to side step in just a halter, stand facing her eyeball and with a whip in hand, tap her side and "push" her away from you. Don't actually push her, just create pressure with your body, and on her halter. As soon as her front and hind end both move over, walk her forward before you try it again.
Once she starts moving sideways, you can start doing leg yields. When you get to a corner, cut your corner short and walk down the wall ten or so feet away. Then use your inside aids like your outside aids, tighten your inside rein to create a "wall" and using your whip, tap her sides. After she moves over a few steps let her straighten out.
When you start doing haunches in, as you're rounding your corner, don't let her straighten all the way so you come at the wall at an angle. Then you use your outside rein to create that "wall," and your whip on the outside to have her move over. Use your inside rein to straighten her body out if she tries to turn her head and go straight.
Also, it helps if while asking your horse to move laterally, you move laterally with them, crossing your legs over when they do. I'm working on lateral work with my mare right now too, it's a LOT of fun, and it's a lot of work for them so make sure you keep the sessions shorts and sweet, and give them enough time to warm those muscles up. Have fun!