It's what she's been taught. She has trusted Yawn implicitly.
Yawn has presented a certain (false) lifestyle, and said that that it is easily achievable by following the simple steps she proposes.
The product are of unprecedented quality, and will sell themselves once people have tried them.
Nurse has a wide circle of friends, family, colleagues and acquaintances, all of whom will be supportive, and will kickstart her business by becoming her first customers (and regulars, since they will be seduced by the sheer awesomeness of the products).
From then on, Nurse will not only rapidly recoup her initial 'investment', but start expanding her empire, as ever greater numbers of people fall over each other for a piece of the action.
The fact that this 'done deal' is not reflected in reality can only be down to fact that Nurse's friends are strange, unsupportive and small-minded people who cannot grasp the greater picture.