I like this theory. My theory
Madotsuki 14 years old – events in the world of dreams, in a coma
Madotsuki 16 years old – IRL, out of coma
Parents died in an accident and Monoko didn’t survive in it too. When Madotsuki woke up, the first thing she saw was mutilated body of Monoko and terribly twisted hands - hands of her parents. The girl was strongly shocked by what she has seen.
Her teacher on the piano Masada-sensei, who was suffering from drug addiction, became her guardian.
Madotsuki fell in love with her friend Poniko, who was an ideal of the girl for her. Madotsuki dreamed to be like Poniko, but she was afraid of her feelings, because she knew, that the society would condemn her for wrong love.
Monoko’s sister, Monoe, lost her mind because of the death of her younger sister and she blamed Madotsuki. She wanted revenge and tried to kill Madotsuki, but when frightened Mado was trying to defend, she accidentally killed Monoe with help of a knife.
One girl was in love with Madotsuki. She was somehow connected with the birds and perhaps her name was Tori. But these feelings were either never found or rejected (and that's why Tori-girls pursued Madotsuki in her dreams and they wanted to put her in space without any exit, they were trying to make her get out of sleep in the game. Perhaps they were trying to did it, because they didn’t want to let Madotsuki find her beloved Poniko. It was jealousy)
Then she saw everything that happened in Yume Nikki. Madotsuki found Poniko in her room, which was more lighter, not so closed. As a result, the appearance of Uboa embodied all Madotsuki’s fears. When she have been moved in a terrible place without an exit, she remembered everything untill suicide IRL. In the end she jumped out the window again - this was the way to help her get out of the coma and to get away from all of those dreams.