I have a BC/GSD cross, a big lad who came from rescue kennels and can take a dislike to other dogs if they bark at him. He's got a damn good memory as well, never forgets who's barked at him in the past. So if I walk him somewhere quiet, I let him off lead but call him straight back at first sight of any other dogs, and if they come towards us I draw him away. I get quite cross when other owners leave their dogs free to bounce up to mine, despite watching me put him on a lead and walk away, then get all huffy when he barks and lunges - I've even had people telling me he should be muzzled. Excuse me, but
I'M the one whose dog is on a lead and under control, legally if the dogs fight, it will be your responsibility, not mine!!! If I am walking him somewhere busy (or near a road, as he's scared of cars and has a fear-aggression response to them) I have him on a 30ft training line, and can reel him in if anyone comes close (being half BC he also tends to chase runners and cyclists!). It's not other people's dogs I worry about, it's mine.
Piegonpie, mine was traumatised by his kennelmate at the rescue, so I totally know how you feel about your poor girl