Correct me if I'm wrong but if I remember correctally, a tarot deck chooses the person. So even if the deck were purified it wouldn't work properly for the person.
That particualar indevidual must select a deck on thier own based on the vibes given to the indevevidual by the cards. Second, once a person's energy has been put into the cards, this sigenature as it were, will remain there perminatly. A tarot deck can't be clensed of all energy other wise it becomes not only useless, but a deck of regular, playing cards with an extra suit.
To cleance the cards a simple spell is needed and some sage should be burned as an extra measure to ensure that they are clear of all negitive energy. Oh by the way to prevent negative enrgy build up from readings, use the spell and apply a touch of body oil to your hands and shuffle the deck. This should only be done once, the scent that works the best is lavender, gardania and jasmine also work well, I've used all three in the past. If you're unsure of which to use, go with your instincts, chances are they will lead you in the right direction.
The spell...
Elements of Wind and Fire
Bring to me my heart's desire
Water, Earth, may wish forefill
Strong my magic
Strong my will
Within there four elements fourefold
The power goes and so will hold
These cards tell both future and past
Bring it to me both true and fast.
The other option is to wrap the cards in a shard of silk that has been purified, and place the bundle in the moon light.
To purify the sham, rub your hands in purified water and wad up the silk, your hands should be damp not sopping wet. while you do so make sure that you have some sage, franck incence, rosamarry or tyme burning. This will aid in the cleaning and boost the effectiveness of the session.
So give it a try. As for your friend, get her a gift card, or some cash. Take her to a magic shop or book store and have her pick a deck. Don't give her your old one.
Bon Forchuna,~Stel~