At any point when she is rotating, whether you see it going counter-clockwise or clockwise, you should be able to tell when her back is facing you and when her front is facing you. Even easier is to tell when she is facing directly to the left or directly to the right. Therefore you should be able to piece together four directions in sequential order (back-facing, right-facing, front-facing, left-facing = clockwise ; and vice versa) and logically deduce which way she is spinning. This is no optical illusion or "brain test" I'm afraid.
Yeah, I guess I don't really get how it works because for the illusion to fool us, it seems that for every still image in the sequence there should be at least two interpretations of what position the figure is in, but given that the leg and the arm are in different positions, it seems like there is only one correct position for every still frame in the sequence. So it's a little confusing. To me, her right leg seems like the one that's not touching the floor, so if it was rotating the other way, the left leg would not be touching the floor? Very confusing. At the moment when she's facing to the side and not directly from the front or to the back, then those figures might be ambiguous: either the left leg or the right leg is extended, but nothing in the outline forces our mind to see it one way or another. But the other positions seem to only allow one interpretation.