Sure. As for a saint, you can pick any saint you wish. You might look at your friend's life circumstances and choose a saint who has a particular interest or patronage in those areas (e.g.,
St. Joseph for a husband and father,
St. Thomas Aquinas for a teacher). Some "all-purpose" saints for conversions might be
St. Monica, mother of
St. Augustine; and
St. Jude and
St. Rita of Cascia, patrons of impossible causes.