Songwriter

[Sonia]

A term commonly misused to describe an American [actress]/model/singer such as [Miley Cyrus] or [Hilary Duff] who writes her own songs.

Proper usage would be an educated individual who makes his/her living by writing both or either the music and lyrics for songs.

[Sommer]

A person who writes popular songs or the music for them.

[Monty]

Someone who can [write] music, but isnt talented enough themselves to [sing] the songs. They have to get someone to sing it for them. Or the [exact] opposite of a person who sings but arent smart enough to write the songs themselves.