Tom if you can find a friend or neighbor with a similar plant to what your wife wants, just ask for a cutting. They start really easily from cuttings, too.
As to dwarf, they're not so common amongst Brugmansia but as Hetty said the Daturas (close relative) are smaller. Still, your wife can readily prune it to stay whatever size she wants. They take very kindly to pruning, and in a few years, just start another plant if the old one gets too stunted-looking or woody. Btw, we have a whole forum for Brugmansias - click on here:
http://garden.org/forums/view/...
