This is because she was indisposed. She was out of body doing astral travel when you attempted to connect with her. This is in preparation for her transition as she is, in a sense, working up to it. So she will be reachable later on during your session if you come back to her at the end, and that would be the best approach here, to get the work in. It will be helpful still. Even though this is a positive sign, she is still holding onto physical existence and your work will be instrumental in helping her transition.