She's certainly not wrong, Gertrude Lawrence didn't have the greatest voice in the world, and as a result Anna is not a very big range. They're good songs that she sings (Hello Young Lovers and Shall I Tell You What I Think of You are among Rodgers & Hammerstein's best), but it's not a vocally demanding score.
"Contentment, it seems, simply happens. It appears accompanied by no bravos and no tears."