Maybe it was just simple as being startled by this dog. If she is OK in other dog's presences it may have been just a fluke. I would just keep an eye on this and yes, if she sees another dog: treats, treats and treats, especially with this particular one that scared her.
Deja, GSD, sable WL, female, born 11 / 2013
Cam, Rough Collie, sable, male, born 8/2015