We are biblically forbidden to participate in exactly what van Praagh does for a living. This is necromancy–calling up spirits from the dead-- and there are several passages in the bible that refer to it. See Dt 18:11-12: Nor charmer, nor any one that consulteth pythonic spirits, or fortune tellers, or that seeketh the truth from the dead. 12 For the Lord abhorreth all these things, and for these abominations he will destroy them at thy coming. Or take a look at Lev 19:31–31 Go not aside after wizards, neither ask any thing of soothsayers, to be defiled by them: I am the Lord your God.
The Catechism makes it clear:
2116 All forms of divination are to be rejected: recourse to Satan or demons, conjuring up the dead or other practices falsely supposed to “unveil” the future. Consulting horoscopes, astrology, palm reading, interpretation of omens and lots, the phenomena of clairvoyance, and recourse to mediums all conceal a desire for power over time, history, and, in the last analysis, other human beings, as well as a wish to conciliate hidden powers. They contradict the honor, respect, and loving fear that we owe to God alone.
Pray for the repose of your mother’s soul, offer up a Mass for her, and pray for souls in purgatory, by all means. But please do not open yourself up to any sort of divination. It is very spiritually dangerous.