two suggestions:

1. with her resting heart rate increase - could she have been over training. The resting HR can go up when you've been over training - along with the breathlessness and dizziness when exercising. Can seem crazy as symptoms can come on much earlier that you'd expect for an athlete's level of fitness.

2. What about seeing a non-medical health practitioner. As a chiropractor, I have seen people with weird & wonderful symptom patterns that had some elements that looked sinister & other that seemed trivial - all in the one person. Many have done the rounds of medical doctors often with non conclusive diagnosis or advice. Once we help their nervous system start coordinating and controlling the body better again, people heal and recover. Obviously, you'd need to see a chiropractor for a full assessment to see if this was the case for Katie. If you would like to know what questions to ask, you can PM me & we can talk further.

Good luck at this stressful time.