Sickle cell beta thalassemia means that both beta globin genes are affected. The severity of the condition depends on the severity of the beta mutation. If it is a beta + mutation some normal hemoglobin is produced and the severity is not usually enough to require transfusions. If the beta mutation is - or 0 then the child may require transfusions. A hemoglobin electrophoresis test can determine the difference. If any HbA (normal hemoglobin) is found, then it is not the more severe variety. The more severe type manifests as sickle cell disease
Although it isn't a conclusive method, the overall health of the thal minor parent may give some clue to the manifestation in the child, so if the thal minor is mild in the adult, it is more likely that the child would not have the more severe condition.
How old is she? Symptoms usually appear during the first year when it is the more severe condition.