Does the content creator bear the sin of music being placed on the content she writes, even though she does not place the music herself and does not request it?

There is no harm in writing permissible content. The sin of adding music to the written material falls on the employer, not on the writer, because the writer's responsibility is limited to what he writes. Allah Almighty says: "And every soul earns not [anything] except for itself, and no bearer of burdens will bear the burden of another." The employer is advised to avoid music and suffice with non-musical sound effects.