Original sentence: She has won first prizes for Image of the Month from the Garden Photographer's Association (part of the [Garden Media Guild])for the months of: September 2008, December 2008, June 2009, and July 2009
Edited sentence: She has won first prizes for Image of the Month from the Garden Photographer's Association (part of the Garden Media Guild)for the months of: September 2008, December 2008, June 2009, and July 2009