I was diagnosed with both eczema and asthma, experienced terrible fatigue, and have had a subnormal temperature since I was a child.
I actually have Lyme Disease. That caused my "asthma" and fatigue and my low temperature. I think it is the cause of my eczema, but am only 4 months into the treatment; so all of my symptoms have not yet resolved. I was bit by a tick when I was 7, but it took about 30 years to find out the cause of my problems. Hormonal changes can bring on the symptoms---they certainly did in me when I was 13.
If she does have Lyme, she needs to be treated for it with antibiotics as soon as possible to return to health. The only catch is very few doctors really understand it, and most of the commonly used tests for it produce false negatives. So, you have to find a doctor who knows what they are doing with it or is willing to learn. If you post on the Lyme board, and tell us where you are located we can give you some names and testing information.
Another thought regarding the low temperature and thyroid symptoms but normal blood work--this is known as Wilson's Thyroid Syndrome. Raising her blood temperature can help it. This problem is caused by a T3 thyroid receptor uptake problem at the cellular level; blood tests can't check that. Her body temperature should be consistently below 98.6 if this is the problem.
Before I was diagnosed with Lyme, I received the treatment for this and it definitely helped. This treatment alone resolves these types of symptoms in some people, but again you have to find the right doctor.
Please just let me know if you want more info on either of these!