It sounds to me like your friend could have posttraumatic stress, which, aside from all the psychological distress it creates, can also lead to all kinds of functional pain and digestive issues, generated by big, opposing swings of neurohormones flooding the bloodstream, leaving behind pain-generating kinins collecting in the tissue.
Don't forget, the catalyzing event or events don't have to have resulted in something "serious" - they just have to have scared the daylights out of her, prompting an overblown survival response that, at least in your friend's case, can't seem to wind down or shut itself off on its own.
So I'm pretty sure this is PTS. I recommend she start out with some fairly low-key self-regulating, mood balancing and spirit-lifting imagery. She could alternate between the Healthful Sleep imagery at night and the Relaxation & Wellness imagery during the day. After 2-3 weeks, she could then add the Healing Trauma imagery to her daily routine.
It would also be great if she could further potentiate the benefit the guided imagery can provide by also availing herself of some biofield therapy - Healing Touch, Reiki or Therapeutic Touch. We know from studies with traumatized Marines that this kind of work, combined with imagery, is very effective and helps remediate symptoms pretty quickly. Each one of these methods has a central website where you should be able to find a local practitioner in your area.
Some therapeutic massage would also be great for helping to manually move those kinins out of her system.
And at some point, she might also get some help for releasing the distorted cognitive assumptions she's made about the cardiac scare with one of the alphabet therapies: EMDR (Eye Movement Desensitization and Reprocessing), TFT (Thought Field Therapy), SE (Somatic Experiencing) or EFT (Emotional Freedom Technique).
I hope this helps.