The OP can’t be certain this cousin is doing anything truly having to do with the occult, rather than just trying to submit herself to the good and true as she has the light to see the good and the true, but it would not be acceptable for the OP to assume it is OK, either, let alone to participate in an effort to be “fair” or “open-minded”.
The OP definitely has the right to have her cousin respect her quest to find the good and the true, though. It is one thing to engage in religious debates, and another to demean another person that claims to be doing his or her best to live a life of spiritual integrity and goodness. Mocking someone else’s belief crosses a line.