I think focusing on yourself as the problem isn't really the right idea at the moment - you need to make some progress before you can gain any confidence. There's also some advice on earlier posts that's a bit out of date - you can't reinforce fear by comforting your dog, and pretty much all contemporary behavioural modification programmes are going to involve treats.
There are two things to address: her emotional response, and her behaviour. The emotional response is harder. You seem fairly certain it's fear, but if she can cope with cars crossing in front of her, then that's a very specific fear. Can she cope with cars coming from behind? Or is it any cars on the same road?
Changing an emotional response can take a very long time - you don't say how long you've been working with the behaviourist, but all good ones will tell you to start by removing the source of stress as far as you can. Can you drive somewhere and then go for a walk? I know that's not possible for everyone but it would allow you to get her out without raising her stress levels every time. Things like desensitisation/counter-conditioning come next for a long-term change, but first you need to try to find a way of lowering her stress in a routine way.
The second element is the behaviour, and you can address this first through management, and second by giving them an alternative behaviour to do. Management is simply about not letting her practice the lunging - again, avoiding cars as much as possible. How much does she weigh? If you can't drive her somewhere, can you carry her for a while in really tricky places?
I know how hard this is, and I'm sure you're trying almost everything (stop popping the lead, btw - it just adds to the fear - while the excitable voice just adds to the arousal). I'm not a behaviourist, but I have a dog who has arousal problems so I'm reading a lot as well as working with behaviourists myself.
The one alternative behaviour that has really worked for my boy's reactivity really surprised me, and that's heelwork. Look at me games are fine when they're under threshold, as you've already worked out, but once he's out on the end of the lead it's way too late. Teaching him to walk to heel means I can put him next to me whenever a possible trigger comes into view. He's much less likely to notice the trigger, or to go stratospheric, when he's focused on a treat; he can't bark and lunge AND walk to heel and be rewarded; and he's already exercising self-control. There are very few things now that I can't get him past so long as his brain is present enough that I can call him back to heel (not always possible, mind you). I'm not suggesting this is a straightforward transfer, but it might be worth a try.
It was very difficult for me emotionally to make the changes I needed to do, but now our routine is far less routinely stressful for him and he's able to respond and engage so much better than he could when he was going bonkers on every walk. The days are harder for me, and I'm more isolated, but I can see the changes and I can begin to believe that things will improve enough for him that they'll improve again for me too. Best of luck x