When the spell checker starts, Orca should read the word that has been misspelled then the context in which this word is found followed finally by the correct spelling.  It should then spell this word and report the button that has focus.  
Example:
Spell Checker: 
broown  
the big broown fox jumped over the lazy dog
suggestion: brown
b r o w n
change button. 

Obviously, if editional words are spelled incorrectly, the spell checker window title does not need to be spoken as the output should be quick and to the point. 

Other information:
The best screen reader to tackle the usability of the spell checker is unfortunately Jaws for Windows.  In my opinion, you should not only copy this functionality, you should built upon it.