My mother has pneumonia. ultrasound shows pleural effusion. fever has subsided but there is heavy breathing. is it due to pleural effusion ?

Pleural effusion : Yes. It could be. Either the pneumonia with subsequent filling of the air spaces with infection could cause the heavy breathing or the pleural effusion that is outside of the lung could be compressing the lung and causing shortness of breath. If the fluid is large enough to be sampled, it should be. This is important to rule out an infection of the fluid in addition to the pneumonia itself.