What is this mean " LVEF - 45% ~ 49% " ?

It means that the blood being pump into the heart is mildly depressed. It should pump at 74 % which would make it regular or normal for the individual.

Left ventricular ejection fraction is 45% to 49% Left ventricular ejection fraction (LVEF) is the measurement of how much blood is being pumped out of the left ventricle of the heart (the main pumping chamber) with each contraction. 55-70% is normal, 40-55% is Below Normal, Less than 40% May confirm diagnosis of heart failure, <35% Patient may be at risk of life-threatening irregular heartbeats. So she is a bit below normal so her heart function is slightly less than it should be. The LVEF may be lower when the heart muscle has become damaged due to a heart attack, heart muscle disease (cardiomyopathy), or other causes.

I would say ask him about it. If she feels ok and isn't having shortness of breath, she may be ok, but he will explain it if you ask. I'm guessing its something to do with the left ventricle and how its working. I'm not one who ever had to read ecgs so I'm not an expert.