That is a familiar problem, I have the same with my pup, but her issue is that she is lazy.
My other dog, he is 1,5 years old, is very aware of his surroundings as well when we go out and can be very jumpy specially with loud sudden sounds, he has always been that way.
You mentioned you could be nervous at times as well when you walk her? THe dog probably, most likely, notices that as well and gets nervous because you are. I have the same issue, though what I do now before we actually go out is some breathing techniques or yoga or just close my eyes and have a moment of quietness before we go out. If I feel calm, relaxed and excited (till a reasonable level) about the walk, I noticed my pups were reacting different as well.
Walking just on the leash to relieve themselves can be dull for dogs, not every walk has to be an adventure, but you could try to make the walk more interesting for the dog.
What I try to do with my dogs to keep them focused on me or my other half, is that at random I make them do the basic tricks (sit, down, give paw, and so on), or suddenly pull out a toy to play with, or suddenly go for a short jog. I also try to take a different route each time, it does not have to be a complete different route of course, but at times turn right instead of left, or go straight ahead.
My male dog, the 1,5 year old, has been attacked several times by other males off and on his leash. He has the tendancy now to react before anything happens. We are correcting that at the moment by occupying him and keeping him focused on what we may or may not do during the walk.
I am training my dogs with the clicker training, it takes adjusting at first, but after it is a wonderful tool.
With Rascal, the male dog, I clicked everytime he would take a step past any dog or object and he is not reacting to it. It takes time and patience and we are still not there but we are slowly getting there.
My pup, Alice, has a fear of bridges, it is a terrible thing living in Amsterdam with all the canals and bridges and a strong pup of already 23/24 kg not wanting to walk, but I did the same clicker and treat and distracting her routine as I did with Rascal and it is working.
To sum my super long post up:
-Go outside with a relaxed calm state of mind, try to be as relaxed and calm as possible during the walk, you own the walk, the walk does not own you!
-Make the walk interesting and challenging, mind that not every walk has to be that way, but changing routines can make it interesting again.
-Rewards! Reward every good behaviour she has, bend the undesired behaviour into something you want.
-Let her confront her fears one at a time until she stops reacting.
As example; Rascal used to love chasing big birds, what I did at some point was just walk past the birds for a million times, until the birds suddenly were not that fascinating anymore.
sorry for the long post hope you find some helpful!!