In message .com,
texas_gardener writes
Hi: I'm trying to find a hedge that my grandmother had in Oklahoma.
It's about 4-5 feet tall, and is full of little white flowers. I've
been searching for it in seed catalogs but haven't found anything that
I think might be it. Was it baby's breath or bridal wreath? I'm not
sure. Any help appreciated --

Baby's Breath is (at least some of the time) Gypsophila. I don't think
you could grow a hedge from that. Bridal Wreath often applies to Spiraea
and particularly to Spiraea x arguta. You can treat that as a hedge, but
if you want the lots of little white flowers it would have to be an
informal hedge; if you clip it formally you'll lose most of the flowers.

There are other hedging plants with white flowers, such as privet,
blackthorn or hawthorn. Quite likely you wouldn't consider the flowers
of blackthorn or hawthorn to be little. It's perhaps not so clear cut
with privet as with Spiraea x arguta, but for flowers privet is also
best treated as an informal hedge.
--
Stewart Robert Hinsley