The invisibility ends as soon as Jacob touches her. There's no reason for her to hide when she can't move and the jig was up. When her appearance manifests again Jacob would find that she was able to roll over, away from the pile and away from Jacob. His foot is perilously close to stepping on her tentacle, which is shaking from stress and worry.

I know I am lucky. You are a true friend, and I do not deserve your kindness. It's not because I don't like you that I want you away. I... felt your fear. It was brief, but in the moment she was looking for the thoughts of the intellect devourer, she felt his panic in that moment.