Steering problems.

I'm finally putting my head on the chopping block.
I have 5 year old project horse. I've had her for about 8 months now. When I got her she was green broke & had a lot of bad habits. We've worked through most of them. However, when I get her up to a canter she starts fighting the bit. Be it in the arena or on the trail. I can get her to turn, but it is extremely wide. She pulls the bit, head tosses & doesn't watch where she is going.
When she is at a walk or trot, she responds nicely. I ride her in a a D ring snaffle and what I was told is a reining bit (its a snaffle with about a 1 inch shank. She seems to respond about the same in both bits. I'm what I would consider a advanced beginner. I've been told I have a good seat & know how to respond when the S%*& hits the fan. I don't have a lot strength in my one leg because of an injury so my leg cues aren't that great.
Any suggestions to make her respond better.

Why do you switch bits? The "reining bit" sounds like a Tom Thumb, which I don't like, but why do you switch them, especially if she responds the same?

The leg injury I expect has a lot to do with your problem. As an advanced beginner, it's likely your seat isn't as stable at the canter as at the less active gaits, and therefore you're just not steering as well at that gait. If you can't use your legs effectively, you have 2 choices: either carry a whip to reinforce your leg aid on the weak side (no, this is not abuse, folks) or learn to use your seat/weight for the aids. The one thing you don't want to do is rely more on your hands.

Do you have an instructor?

What is her canter like? Even cadence? Is she balanced? Are you balanced? Hands quiet? Loose rein? Saddle fit (not pinching when she is reaching forward)?

My horse does the same at the canter but I don't have a problem leg. My horse has a balance problem. She is a young horse (4 yrs old) that I broke last year spring. This year we are starting jumping hopefully and so I have been working on her balance.

I do lots of circles, shoulder ins and flexing at the halt walk and trot. This gets her suppled up and listening to me. The I start up the canter. I first do a shoulder in then release and cue her. Then I know I have her attention and I have control.

Like I said I practise lots of circle and also at the canter I do simple lead changes. She is getting more and more balanced and she is able to control her body more.

Hope this helps

Sugar

Get her better at the walk and trot. I know you said she responds nicely but what are you asking her to do? If it is just simple turns then try half passes and serpentines where she has to shift her balance more often. Lope in straight lines and make sure she is balancing well and there are no soundness issues. The best way I know to improve a canter is at the walk and trot. If your horse is perfect and able to do advanced manuevers at lower gaits getting faster won't be much problem. If you try to fix the lope at a lope then you will make the horse tense and fast and frustrate both of you.

I would also suggest doing more work at the trot. Do lots of long trotting and steering. Don't just do the same thing over and over again. Make it unpredictable. I had the same problem with my last horse, he wasn't responding well in the canter. When I started focusing on steering all over the place (in an arena or field) with no set pattern at the long trot he suppled up really nicely and it transitioned to the canter.

I ride my other horse in the reining bit. Its the bit she came with. It isn't a Tom thumb, but works very similar to that type of bit. Not my 1st choice, I prefer the D ring. The D ring is my sisters & I borrow it when I can, but if she is riding I can't use it. Her saddle also fits the horse (Willow) in question better than mine.
Willow was trained in a Hackmore.
I haven't really bought any tack for her yet, cause I trying to see what works 1st.
I'm not opposed to using a crop. I've used my hat before to re-enforce a cue. I'm just not sure its really an issue of her not knowing what I'm asking since she does do the turn (its just real wide & with a lot of protest)

I do have a balance issue & notice it more when cantering. I don't think its just me though. My sister (who is a way better rider than me, and has tons more experience) has ridden Willow and had the same problem.
When we are in the arena I work the fence, do circles, roll backs,figure eights, & zig zag. I try to be unpreticable & not always ask for the same thing. We've run the poles & barrel patterns. She swings wide on the barrels too even though she knows the pattern.
I know what changing leads is when I see it, but how do I get her to do it?

She has a nice canter & trot. Very smooth & even. My saddle might be pinching her some. I haven't had my vet look at her, but my trimmer didn't think she had any soundness problems.

Yes, I've thought about calling my friend who is a trainer out. I've taken lessons from her before & I'm sure I could use some polish. If its something I can work out on my own though, I would rather try that 1st.