If the tiredness is only a recent phenomenon, I am inclined to agree with the doctor that it is the result of a recent illness. Because her Hb is decent for a minor, unusual tiredness should not be a regular aspect of her life. Her test levels are all good for a minor and her folate is normal and her B-12 is at the high end of normal (slightly above normal is nothing of concern, and in fact another site lists the high end at 914). The only thing of note is the high RBC count. Do you also have the results of a reticulocyte count?
Discussion: Spleen size can be felt in a physical examination by the doctor. If it is bigger than normal, it should be easily determined. There are two reasons why breathlessness could be caused in this context (if it is not the result of a recent illness). One is that the spleen is enlarged and pressing on the lungs, thereby limiting capacity. Again, this can easily be tested using spirometry. Even if it isn't asthma, if there is a physical limitation on lung expansion caused by an enlarged organ pressing on the lungs, lung capacity will be lessened. The other condition that can affect lung capacity is extramedullary hematopoiesis , a condition where in times of low hemoglobin levels, the body will produce red blood cells outside the bone marrow, most commonly in the spleen and liver. This will result in enlargement of those organs. This is very uncommon in thal minors and would not be expected in one with an Hb as high as your daughter. However, because I do know of a case in which asthma-like conditions have been created in a thal minor, I do mention this possibility. If the breathlessness continues, I would ask for a lung capacity test to see if the lungs themselves are a problem. If this proves to be the case, spleen and liver size should be determined to see if an investigation along this line should be taken. The reason I also asked for the retic count is because the RBC's are high, which is normal in thal minor, so I would like to also see the retic count, as this gives some idea about how active the bone marrow is in producing new red cells. If this count is also high, there is some possibility that there is a high turnover of RBC's and the destruction of the old RBC's by the spleen can lead to an enlarged spleen. Again, this is not expected in one with an Hb of 11, but it should be explored if problems continue.
Thal minors usually live with anemia to some degree and the result is that they tend to tire more quickly, due to a general lack of oxygen (hypoxia) and will also find that they become breathless more easily than non-thals. On the other hand, you have thal minors like Pete Sampras and Zinedine Zidane who have had great athletic careers, in spite of being thal minors. Sampras has disclosed since his retirement that he did not let people know he was a thal minor, because he felt that if an opponent understood minor, the match would be drawn out in an attempt to tire Sampras, so Pete dispatched his opponents as quickly as possible so this was not usually a factor during matches. But outside of exceptions like these guys, what I hear from so many thal minors is the same thing. Tiredness, breathlessness, numbness in the extremities, and a need for an afternoon nap. I am sure you recognize these symptoms from other members of your ex's family. As a group, we are learning what we can about what minors can do to improve their lives, but there is no easy answer. Low Hb means low oxygen and the body will move oxygen to where it is most needed, but this means some areas of the body end up with less oxygen than required. My belief is that minors have to try and optimize their health through diet, nutrition and exercise and proper rest when needed if they want to see improvements in their health.