You see I can see both sides to this one.
I grew up with a dog aggressive dog...not just one who growled or snapped but one who truely wanted to kill any other dog. Walking her anywhere was a nightmare, as she would start as soon as she saw a dog in the distance. So walks were always on lead well away from other dogs and at unsociable hours. There were rarely any owners with their dogs then, as most dogs just roamed the streets by themselves, so there was little else we could do really. I imagine if back then we had complained to anyone about their dog approaching ours, they would NOT have been very understanding, after all their dogs didn't have the problem, ours did.
I do think a lot of people do still have that attitude and (now I'm going to make myself look like the bad guy here) I'm not entirely convinced they are wrong either. Of course there is no need to be rude to you or to ignore the fact their dog is pestering yours....but really when a well socialised dog comes over to say hello and have a sniff, it really isn't their fault your dog has a problem with this. As long as they at least try to call their dog away (obviously some don't come because that's what dogs are like) or come and get it, there is little else they can do and really why should they....after all their dog is just being friendly. Ok to be polite and considerate most, myself included, would try to get their dog on lead before it even saw an on lead or muzzled dog but if their dogs are running around enjoying themselves, often they will come round a corner and it be too late, as they are already upon the other dog. All you can do really is to ask them politely to come and get their dog.
And before anyone says they should have better control over their dogs, well probably they are right.....but in the REAL world the vast majority of dog owners don't have 100% recall, some have precious little at all but if their dog is well versed in doggy etiquette, then apart from when it meets an aggressive dog, this really shouldn't cause a problem.
So yes I do feel for you, having been in this situation myself, I know it's horrid and no I don't think the other owners should be rude.....but don't be surprised if they are a bit put out because they can see nothing wrong with their friendly dogs behaviour.
Can I ask, just out of interest, what made you take on a dog aggressive dog? Was it that you fell for her as soon as you looked at her? Was it that you have experience in behavioural problems and you felt you could put her right? Was it that the Rescue was economical with the truth about her problems?
I always find it fascinating that some people will choose to take on a dog with real problems when there are many others in rescue with no problems at all, especially in this day and age when any aggression is often seen as the dog being "Dangerous". Of course love or simply love of a challenge do come into these decisions but it still makes me curious. You say she had been in the Dogs Trust for a couple of years, are they giving you advise and support with her problems? For any dog to be in rescue for that long, they must know she has big problems and it would be unfair of them to just let you take the dog and not give you any back up. Did they try at the centre to introduce her to other dogs and if so how did this go? Did they tell you how to control her, what they had tried, what they found successful and what they didn't? As all of these things could be a help to you. Did they recommend a Behaviourist you could talk things over with?
Sorry for all the questions but I'm hoping I'm wrong in thinking they may have just told you she had a bit of a problem but if you kept her on lead and muzzled you could still take her, without telling you the full story and giving you the support and advise you need.