A congenital heart anomoly will not prevent you from working anywhere. It depends on the severity of the condition, and if it impacts her daily life. If she has no effects from it such as: shortness of breath, blue discoloration to lips/skin from decreased oxygenation, fatigue, frequent illness, then it should not be a problem, and I wouldn't even mention it. If it is already well documented in her medical records, then that information will be available to Qatar medical reviewers. She may have to answer some questions about it. If she takes a daily medication to improve her cardiac function, that will be able to be determined with blood testing, so she cannot hide that fact.
However, as Thelonius observed, the goal of screening bloodwork is to rule out infectious diseases, such as TB, Hepatitis and HIV. The chest X-ray will reveal TB, it will not reveal a heart defect, unless she had prior surgery, and a X-ray dectectable implant was placed in her as part of her correction.
ASD: Atrial Septal Defect, and VSD: Ventricular Septal Defect, what laymen call 'hole in the heart' refers to an abnormal weakness or opening between two of the chambers of the heart. It is not uncommon. Children who have large defects either don't survive, or require surgery before the age of 5. Since she has survived to adulthood, probably her condition is mild. Only large defects can be heard with a stethoscope. If she never had surgery, and doesn't take medications, has no symptoms, and there is nothing in her medical record, then no medical staff will be able to detect a heart defect without extensive cardiac testing. That kind of testing is not part of entry requirements.
The question for Qatar is: Will her medical condition place a burden on Qatar medical services? If yes, she will be denied a work visa. Plus the aspect also exists that it is the employment company that will block her, not necessarily the government of Qatar.