Ok, so let's scratch the nanoSim problem, I was planning to buy a Sim-cutter anyway
After a brief search I've come to understanding that there is NO German provider that does not require German address (I've read somewhere that Lyca does not require activation at all but the website does not confirm). So let's assume that we will register it onto the guesthouse that she will be staying in.
So what is the best choice here - Alditalk, since there is a nice big Aldi in the centre of Sassnitz? How possible is that Aldi will send the address verification letter to the guesthouse (I am no 100% sure if it would be admitted since the location is a little bit... agroturistic in nature)