I would leave the plant alone for now. Like most plants peonies will appear to wilt during the day when it is hot, especially in a sunny area, then when it cools for the day revive. I would back off the watering doing a soak every third day. Then start stretching the time. Think of it this way you removed most of the small roots that were providing moisture to the plant. Now the plant must regrow those. Right now the plant is probably living on the moisture it has stored and not on it's root system. If too much water is supplied to the plant those tiny hair roots can rot. Your friend could provide the plant some shade. A decorative pot or even a chair placed to provide shade would be good.