If that's how it'll be (with the French) perhaps a Faure nocturne or valse or something soothing like that--perhaps it would complement the Beethoven sonata nicely. I believe there is a relatively famous "Valse Caprice" in Db major by Faure that is a moderate showpiece with a good spirit.
..or, maybe something by Saint-Saens. The Etude en forme de Valse is an excellent and elegant piece with which to end a recital, again it is flashy but not overly extroverted and bangy. Its refined virtuosity would also be a nice addition to the rest of the program, being a good companion to the Chopin Valse Brilliante.
Besides that, I can't really come up with much...feeling a little unoriginal at the moment!