Demi Lovato credits sister with helping her through the dark days

In an interview with 20/20, which will air in its entirety on Friday (21Apr11), she says, "I had to think of her (Madison) all the time when I was really, really rough. But I just kept thinking, 'OK, set this example for your little sister'.

"There were days where I didn't want to get out of bed, but looking at a picture of my little sister on my little bulletin board was one of the main things that kept me going."