my wife saw a jasmine tree at a local supermarket. I have been trying to
tell her that it wasn't a good idea, since we live in St Louis
(zone = 6b I believe).

You will have to find out which jasmine species it is, if it is a true jasmine
at all. Jasmines are generally vines. Some jasmines are tropicals. Jasminum
nudiflorum is hardy where you are, but it is a vine, not a tree.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)