The True Power, as I know it, is the power of the Dark One. He grants it's use to those who serves him, or perhaps those who he wants to serve him. Lanfear helped discover it and help tap it. She didn't serve the Dark One before that moment, but how long after it did she? How many of the other survivors of the experiment turned to the shadow? Don't know, but from the WoT guide we do know the main researcher with her (the Guide hints Beidomon might have been her aid, or a partner in the discovery) died after it was tapped and the Sharom was destroyed.