That was the hardest part for me, learning I had to relax. In his worse early days, Woolf redirected on me a few times. We would see a dog or a stranger and I just knew 'here we go again, another trip home bloody'. That was before we found the wonderful behaviorist we have now. We started back at basics with OB for Woolf and handling for me, then adding in one of her dogs (Bouviers) as distraction, then her neighbor (who is also helper at club she is member of) pitched in as the human distraction. From there, moving out of the safe little world her training field provides into the unpredictable real world. It took a few sessions of me successfully handling him through the training sessions to realize I wasn't tightening up on the leash, that I wasn't tense all over.
All that to say it took a trainer I trusted, a new set of handling skills for this dog and successfully handling him before I was able to relax.
I will make one suggestion for the river walk. If it is fenced in, that leaves you without an escape route; especially if it is a tight path. There isn't a chance for Loki to pass a dog that isn't inside her bubble. As much as you and she loves that path, it would be better for both of you to walk a different route where she can see dogs, but they aren't with in her safety bubble. Both of you will be able to relax, as her training progresses and your confidence in yourself and your dog increases, you will be able to work closer. To add - if you aren't comfortable with your trainer - seriously find a new one.