did you add it to the database that Dreamweaver is connected to?
Remember that dreamweaver uses the Testing server settings in your site definition for connecting to the database.
If you use a local testing server, you will need to edit the local database to see the new column in Dreamweaver.
Sometimes, Dreamweaver will need a little kick to see new columns. Close Dreamweaver, then using your OS File manager, browse to your site and delete the _mmServerScripts folder (or use FTP if your testing server is the remote server)