Have the quilt finished as is. It is a beautiful piece of work and trying to change anything now will be very difficult, expensive and time consuming. I wouldn't think twice about giving it to your sister - she may just love it! If she doesn't, take it home and buy her something else. It is just one of those lessons we quilters learn - unfortunately there is no fix. Be sure to smile and tell the quilter what a great job she did as it is very hard to make a quilt for a paying customer - lots of stress.