She isn't very adventurous in exploring new foods and is just starting to cook, so simple, straightforward recipes would be best. Thanks!
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How To Cook Everything Vegetarian by Mark Bittman
Vegetarian Cooking for Everyone by Deborah Madison!
Super Natural Everyday by Heidi Swanson. One of the few books I've cooked all the way through and loved every recipe. It's a go-to at least once a week for this mostly meat-free household!
This is an incredible cookbook: http://www.amazon.com/Silk-Road-Cooking-Vegetarian-Journey/dp/1933823402
Enchanted Broccoli Forest by Mollie Katzen. Also wrote Moosewood! Great recipes from her.
HalfPint is a trusted home cook.
Any cookbook by Crescent Dragonwagon.
Plenty by Yotam Ottolenghi
The French Market Cookbook by Clotilde Dusolier
Check out Nigel Slater's books, Tender and Ripe. Vegetable Literacy by Deborah Madison. And another vote for Plenty.
Hard to disagree with any of these books - all wonderful! I have them all.
American Wholefoods Cuisine, Nikki and David Goldbeck -- This is a good book for basic recipes, baking, preserving and covers all categories. Lots of recipes and good results... It's a foundation comparable to The Joy of Cooking.