She may also be getting less forgiving of bad behavior as she gets older. In my experience adult Basenjis adhere to a certain code of conduct when meeting new dogs. Part of that is approaching slowly and not immediately getting in their face. They expect similar behavior from other dogs. A dog running up to them would violate the standard and might elicit a snark and a response. As long as it's not overly aggressive I wouldn't give it a thought. Chalk it up to a good learning experience for the other dog.
FWIW they have a different standard for puppies. They will give them more leeway. Doesn't mean they won't snark at them but it's more like trying to dissuade them -- defense not offense.