It sounds like a case of transplant shock. Keeping the plant out of direct sunlight for a few days should help. Lavender loves the sun and the fact that it wilted almost makes me think that the person you bought it from didn't grow it in full sun.

Rodney

Plants are fragile after transplanting. Treat them like convalescents for a few days, well watered and in a cool place. If it is doing well, then you can put it the sun, but progressively because the July sun can be brutal.