We picked up a saddle to try for my niece last night.  Any words of wisdom in fitting the narrow withered horse?  Last nights ride seemed to roll to the left.  Could it be stirrup adjustment? 

Are the tree could be crooked, do you have pictures? 

The rider could be heavier footed on one side causing the rolling to one side only. But with narrow withers I would suggest a saddle pad with build in correction pads. This will help a lot. WIth fit for the horse and rolling. I know it made a huge difference on my shark fin boy.

i checked the tree to the best of my knowledge and found the saddle to be evenly balanced and looking straight. 

i thought about trying a couple different pads on her tonight.

I had a Circle Y saddle custom made for me about 20 years ago, loved the saddle but no matter what I did or what pads I used it would always roll to the left side, I fought with it for a few months untill I finally gave up, told my friend that I ordered the saddle threw and she told me to bring it in and she would have a circle Y rep look at it when she came in, she looked at it and told me the tree was warped, the rawhide didnt dry right for some reason and it misshaped the tree just a tad while drying, So thats why it was always lopsided, I thought it was me since it was a brand new saddle, Circle Y replaced the tree and it never did the lopsided thing again.