Ah, I love the tarot! What can I say, for the better part of my life I have been a professional tarot reader and astrologist. Although I worked in theatre and in Mentalism (which I still contribute from time to time) for most of my life, during that time I found quite a niche performing readings, and even began lecturing on the subject.
Now, Mr Browning gave you valuable information regarding insights into tarot, although he mentioned looking into cold reading resources. Now, I do not know if you wife wants to begin performing actual readings, or start doing conjuring tricks with her decks, nonetheless, I do not suggest she study cold reading. Now for magicians and mentalists, mind-readers alike cold-reading is a great resource but for those wishing to perform "Shut-eye" readings which I assume you wife is planning on doing, cold reading only over-complicates the process of interpreting the cards.
Each card is like a painting, and as we know a painting is worth a thousand words. Now, who would you rather, take you on an in-depth guided tour of the Louvre; an experienced professional artist who has been trained at an Art school, or a tour guide who simply knows how to talk about the various paintings, yet has no knowledge of art itself. I believe the same goes with tarot, astrology, etc... You need to understand first the systems, the history, the cards themselves. Cold reading is a great utilitarian system, but if you want to give honest sincere readings for others, and use the cards for yourself I suggest seeing the cards as a picture book of life. Looking at the cards as if you were the Fool, taking a journey.
"You will only begin to understand others, when you start to understand yourself"
http://thefoolsjourney.net/stages.htm
http://www.learntarot.com/journey.htm
(these two links above are wonderful sources of information regarding the "Fools Journey", I think that, before you begin dissecting each individual meaning of the cards, you need to realise what the cards mean as a whole.)
I also want to stress what my mentor stressed when I began learning the tarot. IT IS NOT STATIC. The tarot represents life, and life is always changing moving. That is why not one meaning can be applied when studying. Pictures are worth a thousand words, and no two persons will come up with the same vocabulary list. It is also stressed that tarot is an oracle system, that means based on the current situation the cards will come to be based off the energies associated with the questions (that last statement may or may not make sense

)
The first exercise I went through with the tarot was to take a deck, shuffle them, then lay out three or four cards in a chronological order creating a story. Then based off my own intuition & imagination I would have to come up with a story based on the pictures, I would then put this into a journal. This journal with all my compiled "stories" became my own Tarot Readers notebook, that I would look to during difficult readings. These stories provided actual insight into my own life at the time and then could be related to others. The Tarot is like a motion picture you have millions of possibilities for one single plot.
Once you understand that the cards on whole make one story you can begin to understand them scene by scene, the way a film student would begin to study a movie.
You dissect the card by;
-colours
-numbers
-pictures
-symbols
-Also the general scene, such as mountains in the background, deserts, city scenes, etc...
My mentor made me take each card, and list its traits. Based on interpretations by five or six different authors I would then write all the meanings of lets say a number the card contained, such as 7. If you have five different sources giving you their interpretations of a topic you can get a general idea of that one topic. This generalization of the subject then gives you greater leeway into intuitively grasping the meanings attached to the current situation.
Numerology:
http://www.tarotteachings.com/number-me ... cards.html (the meaning of numbers within the cards
Astrology: Cups:Water Signs, Pentacles:Earth Signs, Swords: Air Signs, Wands: Fire Signs. (This helps in relating cards to your sitter)
If you have any other questions PM me or of course anyone else.