If you're asking whether to plant a larger specimen now, or a bare root plant in fall, I would pick the larger specimen and keep watering it until the ground freezes. If you plant one in bloom, the blooms could dry on the plant for added winter appeal. But I'm not very patient, and want instant results. A bare root plant will easily catch up to a smaller containerized plant in the spring. You do know the blooms will turn green, and then brown? Annabelles have a very old-fashioned appeal, I think they would look nice with brick.

p.s. (whispering furtively) I know it's the hydrangea forum, but has she considered dogwoods at all?

Hmmm - like Cornus Alba - Ivory Halo, for instance?