I assume she's crabbing with her butt out. Is that correct?
I had this issue with Essy when she sat. There are lots of things you can do. I held the leash in my right hand and held food in my left hand. I popped my hand out to the left in front of her nose just as she sat. Where the head goes, the butt will follow. If she is heeling this way, you can use a buggy whip or a long dowel rod and tap her outside hip to remind her to get it in. You can use 2 leashes (one in front of you and one behind you held in your right hand).
I'd also work on "get it in". Put the dog on a flat buckle collar in heel position (doesn't need to be sitting). Put the leash behind your knees and hold it in your right hand. The leash must be very tight (no slack at all). Put a treat in your left hand in front of the dog's nose, say "get it in" (or whatever command you want to use) and start to pivot back to the left...just one small step at first. The leash will tighten further and it will force the dog to take a step back. Praise like crazy and give the dog a treat. Now do the same thing and try to pivot 2 steps, then 3, etc until you can pivot in complete a 360 circle. Once the dog understands "get it in" you can use this command when you are heeling. You can use this command as you tap the hip with a whip. You can use this command when you halt. You can use this command anytime to remind the dog to keep it's butt in.
I have tried the "loop around the belly" thing to teach side-stepping. Usually it is done just with a length of leash. But some dogs seem to be much more sensitive than others. Theo was so bothered by it that I decided it was just not worth it. It didn't really seem necessary.
Why not just work against a curb, or set up chairs, or whatever's around, to force her butt in? And then save your rewards for the best efforts. Also work lots and lots of left turns and get her moving her butt quasi-independently.
(Oops: Lydia and I were posting at the same time!)
one other thing that might help is heeling at a really fast pace and doing sudden stops with quick corrections for not sitting fast enough. If you are moving fast enough and require a really quick sit the dog just doesn't have time to get its rump out on the sits. And moving really fast its harder for the dog to walk crooked. You can also do alot of left turns from the sit heel position as you start off. This teaches the dog to not assume you are going to go straight from a sit and since you start always going opposite the way the dog is facing your dog may decide to anticipate and sit facing a direction that it thinks you are going...
Rather than a belly collar some loop the leash under them but Caleb never liked it at all.* I have done something similar to what Lydia has done.* I also do side steps, like a dressage move with them having to stay in heel position telling him to get it in.* Also do it from the front.* The whole thing is getting them to learn how to move the front and rear.* Also can use a long dowel to tap their rear or hocks or just to place and guide them in correctly but that was a toy to Caleb. These are also good exercises to help get good pivots. Works well for the Rally piviots and Utility pivots. So, I do these in lots of different positions--front, side step for them to get into heel, pivoting--all re-inforcing what correct heel position is/straight heel position.
Susan UCDX GRCH Dunn's Marsh Caleb of Waltona UDX3, OM3, RAE Canadian UD, RE FallRiver's Micah of Waltona GN RAE, Canadian CD, RN
It helped Dusty to teach him to spin to his left. When I rewarded heeling or sitting, I cued him to Turn and give him the treat when he's spun 90-180 degrees to his left. He seemed to start anticipating the Turn cue enough to get him to heel straight, and if he's not heeling straight I tell him to Turn a few times and he straightens up.