As an actual professional who does actual therapy with actual anxious people, here are a few suggestions to help her.
Some of the most successful methods of handling anxiety include exposure therapy, EMDR, and cognitive behavior therapy. For best results with EMDR, one needs to find a certified EMDR therapist, and if she is having actual panic attacks or symptoms of them (racing heart, hyperventilation, feeling like she will die, shaking/trembling, etc) this is the route that may turn it around for her. An EMDR therapist can also walk her through coping skills to help her further diminish anxiety – we all have some CBT techniques under our belts, as well as lots of coaching with the coping skills. There is actually a self help book that leads a layperson through a very basic EMDR method – this might help someone having mild anxiety. (I followed a trained EMDR therapist on her quest to climb Half Dome – she used EMDR on herself to make it up the cables.)
If she is anxious but not panicking, perhaps just unable to sleep and having some hypervigilance (jumpy and tense and thinking every noise is a BEAR OH GOD or an axe murderer), cognitive behavioral therapy, relaxation techniques (breathing, guided imagery, progressive muscle relaxation) and some exposure therapy would be useful. She can try a self help route (there are workbooks all over amazon) and if it doesn't help perhaps an actual therapist could get some traction.
If she's just sort of worried and having difficulty falling asleep until she's exhausted, then waking up repeatedly – an MP3 player, someone to talk to to distract her, relaxation exercises, even some mild sleep remedy like a valerian or melatonin or benadryl can help.
Any of these a doctor can add anti-anxiety meds as a temporary stopgap while she works through the fears.
Gradual exposure would run similar to what we do to test gear, but with more baby steps. Sleep on the living room floor on the pad in the sleeping bag. Sleep on the living room floor with the patio door open. Sleep on the back porch with a light on. Sleep out on the grass in a tent with a porch light on. Sleep out on the grass in a tent with the light off and a lamp close by. You only move to the next stage when you can relax yourself at the one you're on. Add in car camping for a while, add in the MP3 player and other assistance if needed in the later stages. Mix and match, different things work for different people.