If it is still a problem :
Try zig zag leg yielding.
Sometimes horses already know where to go when you start the leg yielding and just do the most comfortable 🙄
Go on the centerline and do 5 meters leg yielding to the right , then 5-10 m leg yielding to the left .. and so on.
Even if the leg yield is not perfect the moment you change direction is the moment where your leg aids come through which is really valuable to make your horse supple and through.
Thanks for all the suggestions guys! I will try these exercises. I think our main problem is not enough forward like Maddie said. At the trot we are pretty straight (haven't started doing at the canter yet) but at the walk thats when the shoulders really lead and her walk tends to not be as active and forward as I want it to be so I will work on that and the other exercises and hopefully we will figure it out! :-)
Yes all of those things and keep your own body straight. Ifor you're straight your horse will be likely to follow. It does help as well to think forward and THEN sideways. Forward movement and your horses balance is the most important.
Two strides leg yield, two strides straight, repeat, repeat.
Be a little bit stronger with your outside leg and try to hold his shoulders from leading. Also go into the leg yield quite forward because the slower he goes the more he will lead! try also some other excersizes with him such as pushing his hind quarters in on a 10 meter cirlce or trying a bit of haunches in on the wall, just get him using his hind end more and not so much on the forehand! Hope this helps!