As a piano accompaninest myself, I learned early on, that the singer is always right. The job of the accompanist is to support the singer, and to cover their as* at all costs, and believe me, I've had to do this on many occasions.

Starkeeper: If your wife needs to hear you play the melody while she's learning the song, fine, but typically a pro vocal performance requires that the vocalist carry the melodic line on her own while the keyboard accompanist provides comping chords, fills & 'counter' melodies, and a possible brief instrumental solo. It's is the job of the vocalist to provide the melody. What creates the magic is the musical interplay between singer & accompanist. Accompanying a singer is truly an ART and requires uniqiue keyboard playing skills and senstivity, as your playing must never upstage the Star of the show: the Singer! - Scott