I'm not sure where you heard that but according to the Communist News Network he was (and they never get it wrong. :-P).
All former U.S. presidents and first ladies, along with President Barack Obama and wife Michelle, were invited to Thatcher's funeral, though Obama's official schedule has him remaining in Washington on Wednesday.
http://politicalticker.blogs.cnn.com/2013/04/15/bachmann-headed-to-funeral-for-iron-lady/
Check post 99.