I've heard that she doesn't really have anything to do with the creation of her music at all.
But I have to say... even though I dislike Madonna, I have to defend her if she, as respect77 suggests, just don't write her music all by herself.
While there are musicians who CAN write an entire song by themselves - that kind of requires that you play every instrument used in the song. I used to play in bands when I was younger - I sang and played rythm guitar, and could easily compose a song... BUT I didn't tell the bass player or the drummer what to do... and the more technically skilled guitarist of the band (which was never me LOL) could add things to the song that I would have been unable to do. So - although I was often the one who came up with a song in the first place, the finished product was the result of every band member's work.