Hi Norman
I am going to come at this from a different perspective,
You must have made a good impression on this customer for her to invite you back again, assuming that
you did infact shrink the carpet.
This can only be good news and you must be doing something right (apart from overwetting the carpet
).
Have you been back and checked it has shrunk and not just come of the gripper,if not when you recall check this over.
Do you know what type of carpet it is, if not get this checked it could be a Belgium Wilton if it is leave well alone you are not qualified enough to clean it.
As for complaining a year later,if in fact that is what she is doing, explain to her in a nice but firm manner that you can not take responsibilty a year a later she should have informed you immediately after she noticed it.
I can only think she isn't that bothered about it and you have kept a good customer.