I second what k9 has already said (I think she is a dog trainer if I recall from past posts though! Correct me if wrong!)
Leash reactivity is what comes before leash aggression - and it sounds like you're very much on the threshold. Do you ever let your dog roam free with other strange dogs in a park or field? How does she react? Dogs that pull are often very frustrated at being tethered, which is made worse when you add a stimulus. Imagine your dog perceives a threat - but she can't go anywhere. What mode does she engage? Fight, of course. She sees a threat in the distance and is proactively demanding space. Some dogs just want to sniff a bum but from what you've said, i think your dog might just take a bite out of one instead!
What makes a worried dog more reactive and potentially aggressive is a worried owner. "But I'm not worried, I'm just trying to get her attention". Pulling, yanking on the leash, shouting or sometimes getting physical (note: all negative punishment) are all confirming that yes, your dog should be worried. Your dog thinks like this: "every time that >insert stimulus< is around my owner goes crazy. I better be on my guard!" So you can go about it two ways - pretend you don't care. This is very hard for some. My mother always gets worried around our rather huge Alsatian off-leash when other dogs are in the park. Alsatian looks at her, sees her pack member is worried, has confirmed that X is a threat, and becomes aggressive. When I walk her she looks at me, I look at the stimulus and shrug. I begin to look at my phone or tie my shoes and call her over. Because I'm acting normal, she's normal. Owner isn't worried, she's not worried.
Second option is to distract with toys or food every time the stimulus is present. Instead of thinking "omg my owner is scared and crazy over XYZ, she instead gets happy about the squeaky duck/treat in her pocket YAY!" (note: all positive) and forgets about the stimulus, let alone it be a threat (takes time!). Getting your dogs attention, even if for only millisecond intervals is a SUCCESS! Because. if you don't have her ATTENTION it means she isn't looking to you for an answer. You've proven for a year just to be a hindrance that wont let her protect herself (leash, harness etc). You ignore her frustration and so she will escalate until it cannot be ignored or someone or some animal is injured, maybe even yourself. This might feel overly dramatic but stuff like this happens more commonly than we realise.
Your dog screams insecurity to me. She's insecure about her space (barrier) and when leashed, her lack of freedom to escape. Her overall behaviour is screaming for help and for someone to listen because if no one is listening she's just gonna have to sit in her corner and fight it out. Learning to "listen" is very time consuming. Communicating with a dog is a very unappreciated skill in this modern day. But with a big and beautiful dog like yours OP, you gotta start.
Now I'm not saying taking her off a harness is a great idea haha. But, if she feels entrapped by a leash it's maybe time to try a long line or extendable. In a controlled setup and out of biting range, see how she feels with more freedom. There is no shame in using a humane muzzle while you work on things. See if you can get her attention and recall her. Be forgiving the first few times as she wont know the limit of her freedom. But many dogs with good recall (practised at HOME!) often succeed very well with this. If you HAVE to walk her on a short leash (because she's not very well trained yet) then work on distracting her instead. At all costs, YOU must have her attention NOT the stimulus. It will look stupid to onlookers and it will feel messy.
You're gonna do good, I have faith. I do think you need an assessment to get you on the track and to point out very specific warning signs and a demonstration of how to respond. Doesn't mean you need to invest hundreds, but enough to gain real hands on knowledge.
For the record my background is training bomb sniffer dogs and exotics. There are a million ways to go about training but never forget to figure out the WHY of a behaviour, to be empathetic with it which will help you face a problem objectively. It's never personal. Good luck! <3