You should encourage her. Maybe she'll go from a JW to a New Ager and, no matter how you might feel about New Age philosophy, that has to be an improvement.
My own mom once had a client (she was a caregiver at the time) who's wife was a hip Zen Buddhist Jew from New York about the same age as her. As part of her caregiving service my mom often had to read to the guy and he always chose Buddhist stuff. Pretty soon my mom started remarking how similar the Buddha's teachings were to the Bible and she actually became friends with the guy's wife! She started saying things that were cool, but were totally out of character. She had me get books for her on eastern philosophy and I obliged. For a while, it looked like she was starting to wake up but then... CRASH! The gates of her mind came crashing down hard! She stopped seeing the Zen Jewess and redoubled her efforts to be a good JW. She was about 63 when this happened, so it was probably her last chance.
I don't know what scared her away but to this day I really regret not encouraging her exploration of Buddhism. I could already see the improvements in her character and on her happiness that slight flirtation caused and I'm sure that if she stuck with it, her entire life would have changed and she would have left the JWs. So please, don't be a wise ass and berate your mother for her hypocrisy. Use this golden opportunity to lure her away from the JWs BEFORE the elders catch on and slam the gates shut.
BTW The Secret is just watered down and warmed over New Thought. Try introducing her to authors like Ernest Holmes and Joel Goldsmith. Joel Goldsmith especially is a lot more Christian sounding and uses a lot of scriptures to back up his theology. Being a Bible thumper, your mom might respond to him more readily.