A New Stranger Danger

For the last year or so Coco has been in the bad habit of lunging and barking at strange dogs and their humans.  I'm sure this is a sign that she is afraid (she can be somewhat timid and submissive), but it sure does give people a bad impression of her.

Around people and dogs she knows, she is the sweetest thing on the planet.  She'll turn over and let the dog next door sniff her privacy till the cows come home, but let her see a dog she isn't antiquated with and she turns into Cujo.  She's never actually hurt another dog (and I don't think that is her intent).  She seems to be saying "I'm gonna bark this loud so you stay over there." And it works. Because I won't let her anywhere near those dogs.

I hear that this kind of stranger danger isn't uncommon, and my vet has given me a few techniques to help.  But I will admit, I haven't been the most consistent with her training.  It is becoming obvious that it is needed.  She is getting a neighborhood reputation for being mean.  That breaks my heart.  This dog? Mean?

Does anyone else have this problem? Please tell me I'm not alone.  What have you done to overcome stranger danger?