Sometime people who are perfectionists cannot see their own mistakes. I think it because deep inside they're actually a lot less confident than they would like to believe, and if they admitted to having made a mistake they wouldn't be able to stomach the failure (even if it's not really a big deal).

If this fits your wife, you might want to actually encourage her successes, rather than point out her mistakes. When discussing her mistakes try to make light of them, pointing out how it's not such a big deal and that there are good things to be learned. Just be careful not to become condescending while doing it.