gwu.Table has a size (rows and cols), but the size is not fixed after creation.
So if you want to add a new row, simply call Table.EnsureSize() or Table.EnsureCols() to extend it, after which you can call Table.Add() to add the new cells.
Don't forget to call Event.MarkDirty() in your event handler, passing the table to let the client know you changed the table and it needs to be re-rendered.