I have noticed the lamentations from users of Better Word Count plugin that it doesn’t work in Live Preview. And the the File Info plugin doesn’t give word count for selected text in Live Preview either.
One alternative is to use a small utility.
On Windows, I use Skrommel’s little AHK script which gives the word count for selected text in whatever program you are using. This does work in Live Preview. I assume similar utilities are available for other OSs.
I use it all the time because I often write in programs that don’t have a convenient word counter, but it’s an option for Windows users who are waiting for plugin updates for Live Preview.