I'm so sorry that you and your grandmother are going through this. At least the two of you are together.
But a large garden is a lot of work, and it represents a lot of knowledge. Does Grandmother have any knowledge? She may be unwilling/unable to work in the garden right now, the loss being so recent, but maybe she can give you some guidance in picking the vegetables that are ready to come in.
If you live regularly with Grandmother and want to take on the garden for the two of you, the Sunset Western Garden Book will be a great help. There is a section for new gardeners ("A Practical Guide to Gardening"), a set of Sunset climate maps (Sunset climate zones are much more helpful and precise than the USDA zones), and specific information on annuals, perennials, and anything else you might want to grow. Lots of photos, too, and illustrations.
Just reading through Sunset's website (the garden tab) can give you a general idea of what activities take place during what months of the year in your area, but specifics would be found in the Sunset book.
I'd suggest following through on Stella's recommendations for friends of Grandfather who knew him and his garden, finding county resources on gardening, and looking for a possible county Master Gardener volunteer program. These are usually phone-in situations, but sometimes on-site visits can be arranged. Such a Master Gardener would be able to give you valuable information on the plants in the ground. If you can get a personal visit, be sure to take all kinds of notes and pictures; you'll most likely be inundated with information within 10 minutes. But it's a good inundation, so as long as you have the notes, the Sunset book, and us here at the forum, everything in the garden should work out well.
My condolences on your loss.
Sunset Zone 17, USDA Zone 9