if anyone has overcome the same problem i would love some help as this is the only thing that lets her down and roads are a no go area.
Exposure to traffic adjacent to her field will help her overcome her fear of traffic "over there".
But if you want to acclimate her to being next to (and amongst) traffic then the thing to do is to train her to accept beng next to and amongst the traffic. Here's how:
Put her in a halter and a twelve-foot lead rope and lead her out the driveway toward the road with the traffic. As you approach, she will get excited, so you should stop where she gets excited and disengaged her hindquarters and do a bunch of ground work exercises right there at that place. Continue to practice disengaging the HQ (and other ground work exercises) until she ignores the traffic. Then put her up for the day. Do not leave that place nor put her up until she stops reacting in a fearful manner. That is, only put her up when she has calmed down and accepts the nearness of the traffic - even if she's a mile from the traffic at this point.
The next and subsequent days, repeat the exercise.
If you do this, you will find that you and she will be getting closer and closer to the traffic before she gets excited, until at some point several days later, you and she will be standing next to the traffic. At that point, you should alter the exercise so that you and she take a short walk down the road that has the traffic. Perhaps twenty feet. Start with a very short distance, and use the same HQ disengagement if she gets excited.
Eventually (and gradually) extend the walk down the road with traffic to a mile or more; always doing ground work when she gets excited until she calms down. Then return and put her up.
Gradually, you and she will become accustomed to being in traffic. Then, later on when you want to ride in traffic, she will not be afraid.
The key to this is lots of repetitions which gradually gets her closer to the traffic - and only quitting when she calms down and accepts the nearness of the traffic. She will soon associate that calmness in traffic gets her relief.