Today I discovered the following aphorism in the ancient book "The Zen of Bureaucracy":
"It is better to write a thousand pages than to speak truthfully to those in charge."
Although this saying may suffer from a touch of hyperbole, at its essence, it is as true today as it was 4,000 years ago when first penned. Much as you might be tempted to speak the truth to those above you and as much as you might hate to write a lengthy useless memo, always choose the latter.
Speaking the truth can do no one any good. If your supervisor already knew the truth, she didn't need to hear it and there was probably a good reason she was hiding it. If she didn't already know the truth, you'll just embarrass her and ensure your rapid departure from your current workplace.
If you are young and still feel compelled to write the truth, then bury it somewhere in the middle of your thousand-page memo. No one will ever read it and your conscience will remain clear. Eventually, of course, you will surrender your conscience and avoid such unnecessary work.