What you should get depends very much on what is the aim of the painting. For basic painting "How to paint Citadel Miniatures" and "'Eavy Metal Masterclass" from GW will do nicely.

However if your wife is more interested in making great looking pieces instead of painting gaming miniatures, I would second the recommendation of Miniature Mentor. While they are an online resource, you can pay their subscription service, download all their tutorials (there are a LOT of them) and then end the subscription after the first month. This way you would have an offline source of 80+ hours of material on painting and sculpting available whenever you want it.