Most Helpful Girl
The picture is by a she actually, Miwa Yanagi. Its a really old fairy tale originating at around the 17th century in Europe and was also written down by the brothers Grimm, the story is called Brother & Sister.
So the story basically goes like this to put it as simply as possible:
Two kids are mistreated by their stepmother who is also a witch. The two kids escape into the forest but the witch has already found out so she bewitches the springs in the forest. The brother is thirsty and wants to drink but the sister warns that he shouldn't drink from the springs or he'll become bewitched from it, the first spring would transform him to a tiger and tear his sister to pieces, the second spring to a wolf (which would have the same consequences) and the third spring to a deer. By the third spring his sister was too late to warn him so he turned into a deer.
The rest of the story is also kinda odd, the king follows the deer (brother) home and finds the beautiful sister and marries her, and they live happily ever after until nd the witch finds out after the sister (now queen) has a son that the two are still alive, and so she kills the sister and replaces her with her own disfigured daughter whom she turned to look like the sister. King eventually finds out when her ghost visits the baby son. And witch and her daughter are punished, daughter is banished into the woods and eaten by wild animals and the witch is burnt at a stake. And after the witch dies the brother is transformed back to his human self again and reunites with his sister.
Sorry couldn't really simplify the story any more than that, but its a grim story, just like the rest of the brothers Grimm stories. Why the girl is laying in the lake in the picture though I don't quite know.
Most Helpful Guy
It's from the fairy tale "Brother and Sister."
A brother and sister run away from their evil stepmother. The sister told her brother not to drink from the spring or he would turn into a deer. He did it anyway, and she promised to never leave him. The girl is eventually found by the king, who is out hunting the deer. She agrees to marry him and become queen as long as the deer is not harmed and can live in the castle. The evil stepmother finds out, kills the sister, and replaces her with her own real daughter. The king eventually finds out and the sister comes back to life, spoiling the evil stepmother's plot. This magically cures the brother.
I assume this peace combines the idea of the brother drinking at the spring with the sister being murdered by the evil stepmother. She promised never to leave her brother, so in this twist the doe stays with her after she is killed, thereby fulfilling her promise.
To me it evokes the idea of the foolishness of making promises you can't keep (even through no fault of your own), and the foolishness of someone else naively depending on them.