Jean's given you one example where 'it' could be a light. Or, for example, 'it' could be a camera. If the woman is up on a stage, and a photographer is somewhere below the level of the stage taking a photo of her and the camera is pointing upwards towards the woman, then you could say that it - the camera - 'is aimed up at her.' Or 'it' could be a gun. Or a bow and arrow. Who knows? We've done the best we can with the limited information you've given us!

If she has a light on the ground aimed up at her, this means that the light beam is directed up so that it shines on her.

Can you give us more context?