Importing a shared photo stream into iPhoto creates duplicate photos
to provide an answer to this old question, as it's still good info to have...

1) The best way at the time to delete the photos would have been to view the Last Imported photos and delete them from there.   Not just deleting the duplicates, but deleting all of the photos (basically to reverse the import that was done).

2) What should have been done to import the photos from your wife's phone in to your library is to connect her phone to your computer, and import them from the phone itself, rather than the stream.   This way, you are getting the original photos, not the compressed / lower quality versions from the photo stream.