A few months ago, I experienced the following situation: We (two people) were climbing the last pitch of a multi-pitch route. Near the end, there was a cave-like chimney. Basically a chimney where the opening was narrower than the chimney itself, and the whole thing getting narrower towards the top.
When I lead that pitch, I had no problem going up, noticing that I had to leave the chimney because the top opening was too narrow for my helmet, downclimbing a meter and continuing on the outside. When I was belaying the second, she got stuck inside the "cave" because of her backpack with no way of going up, down or out. The whole situation looked a bit like this (left: side view, right: front view):
Our problem in that situation was that we absolutely couldn't communicate (cave roof between us, open sea to the back, so no echo), and I had no way of knowing what was happening down there. She finally solved the situation by letting go, falling for at most half a meter and then (with great difficulty) wiggling out of the cave. If I had known that she needed to be lowered like 1-2 m, the whole situation would have been solved in a minute, but like this, it took like 15.
While it worked out fine in our situation, what is the generally recommended way of handling a situation where the second seems stuck and absolutely no communication is possible? Also, what would have been the appropriate reaction of she hadn't been able to move?
This is mainly about how to handle such a situation if you haven't prepared specifically. However, recommendations about preparing for the case of such a situation are also welcome, if this doesn't make my question too broad!