"the man adjusting his lens to take just the right frame of her suffering might just as well be a predator,another vulture"

It means that the person should be focusing on ways to ease her pain not focusing on not helping her pain

Sounds like someone is taking a photo of someone who is suffering (adjust the lens of the camera to make sure to get just the right picture (frame) of this person) - and the person describing this action feels that the photographer is taking advantage of the persons suffering -