[Help] Other dogs aggressively barking at mine. Am I doing something wrong?

Hi all! My question might be so basic, but I've never owned a dog before so I'd love your advice. My adopted pup is a little over a year old. She's an all-black, 45 lb chow/amstaff/weimaraner/GSD mix with features that mostly make her look like a petite, black GSD. I've had her for about 6 months, and she's just a quiet, silly, friendly little girl. I live in a building with a huge fenced in yard, and many other dogs. She's got her bff dog friend who lives next door, but for the most part, all the other dogs immediately and aggressively bark at her on sight. Two of the dogs will bark at her through the fence when she is on the other side of the yard. Sometimes, she'll go up to the fence (which I realize is probably not idea) to sniff it out, and gets barked at too. I've started to notice that on walks, there often are dogs who will do the same. Half the time we're on the other side of the street and minding our own business. My dog doesn't seem to be doing anything other than existing in the same space. She never (and I'm not exaggerating) never barks back. What has started to happen is she whimpers ever time we pass a new dog on the street, or tries to run past quickly. With the dogs in our complex the owners have said "oh well they just need to get to know each other." My dog is already a submissive dog when she meets new dogs, lying belly up when she meets, and it makes me super nervous that she'd just get attacked. Is there anything that I, as the owner am doing wrong, or is there anything I can do to help her out? Thanks! via /r/dogs http://ift.tt/2rxxlWx