since this was the wife of your co-worker, there's no way in the world you can say anything in any way that will not change the relationship you have with the man. anything you say will hurt his and his wife's feelings.
the deed is done. do you want her to take the stitches out and redo it? do you want a discount? if you just want to vent, then do it here where we understand. otherwise it's going to be very hard to work with him. all you can do is never use her again. if he should ask you why, tell him your cousin does it for you now.