I take it that you are the Nana in question ? :-) This can be heartbreaking, but there are things you can do about it. One is to get books with lots of pictures, and learn about the animals in the woods. Take her to zoos, where she can see different kinds of animals. Talk about the woods, what is there, what you see. Talk about how the trees make shadows of shade and keep your yard cooler. Tell her that the animals like it IN the woods, and they don't come into your yard.
Do you have a bird feeder, so she can watch the birds ? Where we live, we get lots of cardinals and goldfinches, and they are SO pretty, we all stop to watch the feeder when we walk by the kitchen.
The more we learn about the things that scare us, the less fearful we are. (This is being said by someone who backpacks in the wilderness in spite of being mortally afraid of the wildlife when she goes to sleep -- or doesn't)
When your granddaughter does come, play close to the house. If you need to, make a LINE of somekind that the "animals" won't cross over. Even if it's just a string on the ground, or something -- tell her you put it there because the animals will see it and smell it, and they will know not to come in the yard. (yea, it's meaningless to the animals, but she doesn't know that, and my guess is that you don't have bears or other woodland creatures wandering into your yard like my neighbors do)
Work your way through the fears. That's the best way to deal with them. :-)