You can try to engage her regarding rationality through examples she is not personally invested in. That is, avoid spirits and healing stones and discuss more "neutral" applications of rationality. Discuss cognitive biases, Bayesian probabilities, mind changing techniques etc. Let her rethink her specific "new age" beliefs at a much later stage when she has tools for dealing with it.

Also, I second the thoughts of other people that seeing spirits might be a sign of a serious problem. However, pushing her into seeing a psychiatrist sounds also very risky. Maybe consult with a specialist discreetly? Specifically, I would worry whether she has a condition that will deteriorate if not treated. Otherwise, it can be ignored for a while.