Elsewhere in your letter, you mention that the daughter who's refusing to follow your desires says she has recently committed her life to Jesus Christ. That's undoubtedly why she doesn't want to get involved with this, because she knows the Bible forbids it.
Any type of occult activity (including attempts to communicate with the dead through a spirit medium) can involve us with spiritual forces that are not from God, but are actually opposed to God. On the surface, they may appear very innocent or benign, but in reality they aren't. The Bible is very clear: "Let no one be found among you... who is a medium or spiritist or who consults the dead" (Deuteronomy 18:10-11).
My real concern, however, is for you. Those who follow occult beliefs would have us believe that the next world will be a place of peace and happiness, but this isn't necessarily true. The Bible tells us that eternity is real, but if we've turned our backs on the living God and rejected His Son, we have no hope of heaven. Instead, our destiny will be that place of absolute loneliness and despair the Bible calls hell, separated from God forever.
Don't be deceived, and don't miss the great gift God offers you -- the gift of eternal life. Instead, by faith repent of your sins and open your heart and life to Jesus Christ. He alone is "the way and the truth and the life" (John 14:6).