Prism99

I would machine baste the binding over the edge and then wash. If it's too difficult to turn the binding, you could simply machine baste a strip of white cloth over the edge. The whole point is to cover the raw edges while machine washing.

Edit: It would be best to machine baste the binding over the edge. That way you can be pretty sure the binding will not shrink more than the edge shrinks. When taking the quilt out of the washer, I would take a few minutes to pull on the edges while the quilt is still damp to make sure the binding is not pulled too tight. For this reason also, you may want to lay the quilt flat to dry (on top of a sheet on carpeting, with a fan to speed drying time) and stretch the edges periodically as it dries. Drying in a machine could shrink the binding that has been sewn on.

Edit2: You also need to be sure you use a washing machine that uses enough water to dilute any dye bleeds. Since it's somebody else's quilt, you might want to have them do the washing and drying so you aren't held responsible if there are any dye bleeds.