I think folks who are into reading Tarot cards and tea leaves and the like are still sometimes considered a bit "out there" and even a bit "flaky" by "worldly" standards. It's hard to say for sure without knowing the context of your conversation but I think I'd see red flags too if someone who I hadn't met face to face, brought up the subject of Tarot cards in an online or IM conversation.
I wouldn't see this as a "dilemma"....you're only talking to someone new who has a different life's experience and background than you're accustomed to but if it's the Tarot card thing that's throwing you off, perhaps you could ask her a few questions* that might give you an idea if it was just a passing comment or if she's really into that kind of thing and make a determination from there.
*So your friend reads Tarot cards....how does that work anyway ? Did she do a reading for you? What was that like? Do you think there's anything to it ? etc