You've screwed up pretty bad, don't do anything that will make things worse like trying to get it patched up on the cheap. Tell the owner to book it in to the bodyshop of their choosing, have it repaired to their satisfaction and have the bill sent to you. Mentally prepare yourself for a big number and when the bill arrives pay it straight away without questioning it. Then move on and don't do it again. Then poo through her letterbox.