If you lived in Japan (and spoke Japanese), you would not hear about Hattori these days in the media at all. I cannot even recall when the last time was I heard about her in the sports section of national TV news programs.
After a few minutes of searching on the internet, I cannot find any news about her current activities or retirement. Yet I have found that:
1. Her official blog has not been updated since July 2008. The last entry says "We are very sorry but no comments will be made here for some time."
http://white.ap.teacup.com/michiko/
2. She got married early this year and some people say she is a great housewife type. She's quoted as saying that she would like to have children.
I hate to speculate since you're a fan. So I will leave it at that.