Lameness can occur from having a misdistribution of weight.
If your mare has long toes with low heals and she is on sand being lightly worked I would go ahead and take the shoes off for a setting. Bear in mind that she might be a little foot sore just as you are when you start going barefoot in the summer. Paint her soles with Venice of Terpentine to help. My Morgan has been barefoot behind most of the seven years I have owned him. I have competed with him at a recognized level in hunters, combined training and First Level Dressage.