Reddit mentions of Becoming Vegan, Express Edition: The Everyday Guide to Plant-based Nutrition

Haha, yes, no one wants to be told they have to cook and prepare beans and veggies. So many people today don't even have exposure to fresh food, it's a bit scary.

I'm guessing your niece isn't terribly interested in nutrition but if she is committed to the plan (at least for now) then Becoming Vegan Express Edition is the best book on the subject and covers things like B12, making sure you eat legumes, common pitfalls of the diet, etc.

Brenda Davis (RD), a registered dietitian with impressive credentials has updated her book "Becoming Vegan" and made an express edition that is now out

A larger, fully referenced Comprehensive Edition will be out in the new year (likely February or March).

Davis is a thorough researcher and sticks to solid science. You can trust what she writes.

These links might be helpful:

Vegan staples:

http://www.seriouseats.com/2013/02/how-to-stock-a-vegan-pantry-items-foods-beans-condiments-sauces.html

Vegan nutrition:

http://veganhealth.org/

http://www.theveganrd.com/food-guide-for-vegans

http://jacknorrisrd.com/

http://vegankit.com/eat

http://awellfedworld.org/whattoeat

General Recipes:

http://theveganstoner.blogspot.com/

http://www.theppk.com/recipes/

http://vegetarian.about.com/od/vegetarianfamilies/qt/collegeveg.htm

http://www.collegiatevegan.com/recipes

http://www.foodandloathing.com/2012/10/the-easiest-beginners-vegan-recipes.html

http://www.theppk.com/recipes/

http://vegweb.com/

http://www.chooseveg.com/vegan-recipes.asp

http://www.tryveg.com/

You should be able to find seitan recipes on a lot of these.

Fitness:

http://veganhealth.org/articles/athletes

http://veganhealth.org/articles/protein

http://www.veganfitness.net/home/

http://veganbodybuilding.com/

Vegan shopping:

http://veganessentials.com/

http://www.theveganwoman.com/top-5-websites-for-your-vegan-on-line-shopping/

If you're looking for a book, Becoming Vegan is great.