I can't accept that Basenji's just get this way with age, I've had friends with dangerous/power breeds that got along great with every dog so with proper training I don't see why my girl can't either.
Maybe I'll look for a local trainer.
You may not accept it, but it is not uncommon at all. In many breeds, not just basenjis. As dogs mature, anywhere from 2 to 4 depending on the breed, you can go on every breed board of every dog and find that dogs who were wonderful "suddenly" developed dog to dog aggression. And if that local trainer tries to tell you that you can train dog-to-dog aggression out, run. You can teach your dog to behave. My massively male-to-male aggressive Rottweiler (only big dogs, he let the fru frus chew him up and use him as a nyla bone!) was fine at shows and in public because on a leash, he looked at ME, not them when I told him. But not for one second did I delude myself that I had done more than train his behavior and given the opportunity, fighting would ensue. When I monitored the Pit bull and other breed boards, long time members warned newbies– good the dogs get along now when at least one is young, but don't bet their lives on it continuing. Keep vigilant. And we'd have people say OHhhhh they LOOOOOOVVVVEEE each other, they'll never fight. And sure enough, that'd be the pair that they came home and found one dead or both seriously injured.
Nor can you compare your girl to your friends' dogs. While many may get along, especially with good training and owners, they get along also because they are no dog aggressive. Idiot owners can foster fighting and bad behaviors. But the best of owners cannot make a dog-aggressive dog NOT dog aggressive, they can only train, manage and avoid problems.
Is it however slimly possible that once you are settled and she gets back into a routine you can ease her back to other dogs? Maybe. But the aging from 2 to 3 is so much more likely the issue I'd be fairly surprised.
And now I'll stop, cause this is such a flashback to other tragedies I have seen unfold with people asking, then throwing aside all advice because they can't "accept" their dog is a dog and acts like a dog, where in many breeds dog aggression is more the norm than a shock.