Oh Cal.... just move on... it doesn't sound like she has any long lasting negative issues from this experience... neither should you.

Consider it all part of her sexual journey... without it... she WOULDN'T be the person she is today... sexually or otherwise.. if you love her for everything that she is.. than just consider yourself lucky that she was able and willing to open up to you about such a deep personal thing.. and move on

Good Luck... have a wonderful holiday... give the cousin an extra hug this year knowing that she has helped your wife become who she is meant to be