I also agree about the personality of a sewing machine.
Another cute idea would be to get a.....
sewing machine Christmas ornament
coffee mug with a sewing machine on it
sewing machine music box
sewing machine print fabric
sewing machine anything..... but not the actual sewing machine with the gift certificate or monies in the package with a hand written note or card from him expressing his desires for the monies to be spent on a new machine.
Her heart might already be set on a certain machine for the $400. Then she could use the rest to build a stash of fabrics to try out on the new machine or extra feet for machine....