mountainmom, my concern would be that letting her off the hook about the trips would feed the anxiety, making it worse, not better. Sometimes if you acknowledge that the unreasonable concerns are real by letting them influence choices, they become more of a problem.
Were she my DD, I'd probably work through this using cognitive-behavior therapy principles: facing the anxiety, thinking through which anxious thoughts about the trip are realistic and which are not, practicing strategies for arguing against unreasonable negative thoughts. ("What if we see a bear?" "I've studied bear habitats and I know there are few bears in this area at this time of year." Or whatever arguments are necessary to combat the fear, as a lawyer would rebut a false argument.) For realistic fears, you can help her brainstorm strategies for solving those problems.
I'd also seek to connect her with a trusted adult who will be on the trip, so that if she becomes worried on the trip, she will know who to turn to.
DeeDee
