I don't know of any books really. I learned arc welding at a very young age, probably 8 or 9 (my dad was a machinist, mechanic, boilermaker, civil and marine engineer [actually certified in most]).
When in high school I took advanced machining (3-hours/day coupled with 3-hours blocks of automotive :) ) Then I went to BCIT for Automotive for another 4+2 years, including Tig/Mig and OxyAcetylene course.
So while I HAVE aquired a good set of trades texts, I don't know of any 'books' you can get really.
Welding is a hands on 'art'. It isn't anywhere NEAR as easy as it looks (not to suggest she would have any troubles learning, but I've got friends who THINK they can weld because they have equipment). But to learn from a book and place it in practice are two different things.
Welding takes hours and hours of running beads and joining differet metals so you can get a flow. Much like air brush art does. It takes practice, that's all.
Do her a favour, stick her in a trades class in her spare time, buy it as an 'odd' anniversary present or something, BETTER STILL, buy BOTH of you a training course. Then it turns into one of those cool 'things you do together' gifts.
Get her a set of those little table-top oxy/propane kits, which are EXCELLENT for small projects, wrought art and stuff.
But by all means take a course, get some professional instruction.
I'd start with Oxy Acetylene as it teaches you pacing and penetration. (or was that sex ed?)
Once you get a 'feel' for the comfortable pace and flow needed to weld, you can then learn tig welding to work on aluminum.
It sure is a fun thing to learn though, VERY relaxing and very personal, not to mention HANDY AS HELL!