Stealing is bad, but if the person who got their deck stolen, had done meditation for a while, they wouldn't mind. A deck is just a deck.
I doubt your friend's girlfriend's abilities to use the tarot, if she had to steal the deck..
I have a strange feeling as well, when I'm doing something I don't know that I should have, haven't had that feeling in ages. I suggest to you, to overcome Fear first.
Though I myself use Tarot, there are many ways for divination, the tarot isn't really for "Fortune telling" as such, it's for predicting things if used correctly, and to help others to know what to look out for if they are pursuing something.
I doubt your friend's girlfriend knows how to use the Tarot properly, but I have never met her, so I do not know.