>>>can anyone advise what is best for playing card games
I'm tempted to write "A pack of cards!".
For such a simple task almost any computer would do but my own preference would be to go midway between a laptop and a tablet, by purchasing a netbook. (I've got an Acer Inspire One. If you consider one yourself, you should be aware that there are two different versions, with the slightly more expensive one offering a far better battery life).
However your wife might wish to consider where she'll be playing Solitaire. Despite their name, laptops really require a desk or table to put them on, as do netbooks. If your wife wants to play solitaire on a train, while relaxing in her favourite armchair or while in bed, then a tablet would probably be best.