Hi Masha, im feeling very sorry for you, i empathise like you would not believe.
Ive been a "Dora owner". Here's how i avoided:
killing my dog
my dog killing other dogs
1. Find a dog school - see, you're allready on the right road.
2. Think of this school as a 'etiquette school', its the place she's going to learn manners and etiquette, how to be a lady, and stop acting like crack addict trailer park trash lol
3. Explain to the dog trainers, what you are going to do....
Do the class, but at the distance away from the other dogs, where you have complete control and Dora is behaving as if she has manners. Where she can watch and concentrate on you ignoring the other dogs. With my rottie, it took 4 weeks to get half a tennis court close to other dogs without being a idiot about it.
4. If you hit trouble, ie, she's growling, or barking at another dog, do a quick U turn, and head off in other direction. The idea being to distract her attention away from the dogs, and get her focus back onto you.
5. Ask a friend with a dog, to meet you at neutral ground. Local park etc. Walk toward the firends dog, with Dora on a very loose leash. (sends lovely signals that you are not expecting trouble from her, you are relaxed, thus she should be).
The MINUTE she starts to show aggression "goes stiff, up on her toes, staring at other dog front on, hackles up, growling" etc, U-Turn and walk away from approaching dog. Once she is settled, turn around and repeat. Repeat for as long as it takes her to get the message, that poor manners will not get her anywhere.
Keep her focussed on you, buy a steak cook it well so its less messy for you, cut it into 2mm pieces, keep her attention on you/food as you pass the dog. Tell her she's a good girl for watching you, and not being a 'bitch'. Use her inner pig to overcome her poor manners.
The idea is not to punish, but to redirect her attention onto you, and the food.
Repitition is the name of the game. Serious repitition, till she finds other dogs no challenge. It takes ages i know, and you wish you had one of those happy go lucky dogs like the others at the school. She may well never be a sociable dog, but she can learn manners and not react.
What tends to happen in these situations, is you begin to avoid other dogs, like walking Dora at night, not at 'peak times' in parks, this will re-inforce her behaviour. You must expose her gradually, gently to the situation. Any stupid behaviour is met with a "no" word, and U turn.
If out walking, make her sit or lay down, you have more control over her in this position, than if she's upright. Keep her focus on you, not the approaching dog. YOu may need to do this by crossing over to the other side of the road to get success intially. Mind numbingly boring and repetative Baby Steps is the key to success.
Hang in there love! She'll be able to pass another dog, without being silly one day with practice.