The secret is not a secret at all, it is just wrong. Essentially it says that positive expectation and optimism equal a more successful life. While there is some merit in cheering people up and encouraging them to realise the opportunities available to them, this is not what the Secret does.
It defers all of your life's events' responsibility to you. Got raped? Must have not been thinking nice enough things. All those starving kids with guts full of worms? Clearly just not positive enough! It quickly becomes ridiculous and reinforces the madness that we live in a just world rather than create our own justice through humane moral authority.
What of mental illness?
Try and fight anxiety and depression by all means, but this is superstitious, superficial magical nonsense. Don't give this woman any more money. Borrow it from a library if you have to read it.