Art reflects life and Amy's paintings and writings are certainly no different. Amy was a talented artist and she painted and drew to reveal her inner state:
The sides of the tunnel were painted with a collage of pictures. They were from Amy's brush. I would have recognized her art anywhere. Now Jake released my hand, and I moved closer to the pictures. Familiar faces stared back at me including Grammie, Amy's mom, and Amy herself. There was a picture of two little girls feeding ducks. That was us. We used to walk down to the city park with old bread to feed the birds. In the center was a picture of Jake on his horse. (20.14)
Amy paints the people she loves (like Dani, Grammie, and Jake) and even herself, drawing pictures of herself overweight and thin to express her transformation. She doodles in her diary, too, enhancing the entries. This is Dani's first clue that Amy wasn't sad or depressed or struggling—she painted to express what she felt, and she only painted light and happy moments.
Because of this, the one painting Amy creates of something really upsetting gives Dani her biggest clue:
We both stared at the revealed picture. The rest of the pictures were brightly colored images of people, animals, and flowers. This picture was painted in black, white, and red. It was a mouth taking a bite from the palm of a hand. Blood sprayed from the hand. (27.57)
When Dani sees Amy's gruesome painting, she knows something pretty horrible must have gone down. Amy hid this painting, too, burying it deep in her secret art hideaway. Maybe she didn't want anyone to know what happened to her? Or maybe she only wanted the right people to find the picture and know exactly what she had been through? Who knows? Amy's dead, so we'll never find out.
No matter what, though, Amy definitely used her paintbrush to let the world in. And in this way, she reveals so much about her life after her death.