Depending on how comfortable she is with words and poetry. Forget the music to start with, and concentrate on the rhythm of the words, eg:

When first unto this count-ry
A stran-ger I came

Go through it a few times, then let her sing it to the tune. Let her sing a verse or two, then sneakily join in with the accompaniment on the first stressed beat. Keep the accompaniment in the background.

Alternatively, let her learn a song as:

1-2-3-4 1-2-3-When first ....

I've used both these methods in choirs with non-readers of music.

Phil