Hello, Welcome to HCM, I am Dr. Das
Look, your sister is suffering from alpha thalassemia
It is a defect in hemoglobin
synthesis but is minor in clinical course than beta thalassemia
So, do not worry at all. It is not a lymphoma
. But her spouse should be tested by HPLC study to rule out any chance of homozygousity or dual heterozygosity in their children.
Hope this will become helpful.