Hi Teo,
First I will try to answer your question about iron overload. It is true that many kinds of food can increase or decrease iron absorption. I knew fron dx that I should get iron overload since I was transfusion dependent. I stopped eating red meat and Vitamin C. I drank tea and milk.
http://www.irondisorders.org/diet/
The amount of iron we can avoid is very small compared with what we get when we are transfusion dependent. Then som patients like me and perhaps your mother have hemolysis (the red blood cells burst too early).
If your mother has tolerated 2 units of blood her heart seems to manage that. Of cause it is better if she only needs 1 unit. I have never received diuretics but my heart and kidneys are OK.
You can control the kidney function with the creatinine test. This is a very common test and they have probably already controlled that. Ask for the result and for the reference value of that lab (written near the test result)
The heart should be controlled at every visit to a doctor, who should listen to the heart. There is no blood tests for that but many other examinations like ECG.
Kind regards
Birgitta-A