What is the condition that reduces her blood's ability to carry oxygen.

Sickle cell is a disorder that affects the molecules in the red blood cells, particularly the hemoglobin. The hemoglobin is the molecule responsible for transporting oxygen throughout the body. When a person has sickle cell anemia, the red blood cells are distorted crescent shapes that do not travel in the bloodstream properly and efficiently. As a result, this disorder hampers the distribution of oxygen throughout the body.  

Anemia is the major characteristic of sickle cell disorder. A person with sickle cell anemia has low number of red blood cells that usually begin in early childhood. A person who is experiencing Sickle Cell Anemia will have multiple and repeated infections, and periodic episodes of pain. The severity of this condition varies from person to person but is common in African descents.