Our little flock of mallards have all started to fly. We have one female who seems to refuse to fly. From what we can tell she can fly. We have seen her fly about 50 yards and about 10 feet in the air. But, when it comes to out and out flying way up in the sky she just won't do it. Is there a reason for this? She doesn't seem to be injured and has shown us that she is able to fly. She is about 4.5 months old.