Susan, it looks like an Aster which is in culture (on the Continent) as Aster tongolensis (or farreri?) Berggarten.
There are some look alikes in culture under these name(s) as well.
When I first saw your picture, Aster yunn. Napsbury came into my mind, but I am sure it is not.
BTW, I am searching for that aster already more than 20 years. It was cultivated for cut flower industry in the 60's
in Holland and Germany, but it seemingly diasappeared totally.
Here a pic of A. Berggarten in a garden and one of a flower of a plant of my own which I acquired as Napsbury, but ist is to short for that and thus Berggarten.