Sigrid is a great host; she is very kind and helpful. The rooms are simple but practically equipped and I wasn't short of anything; even air conditioning is installed. Most importantly, however, everything was clean and functioning well.
Sigrid also gave very helpful suggestions to my question about which trekking agency to choose for climbing Stromboli. Thus I now can recommend guide Franco from Quota900, who is a very sympathetic guy guiding mostly smaller groups of just about 10 people, which gives a much more personal group atmospere than elsewhere.
Climbing Stromboli is technically not extraordinarily difficult, but it does require a good physical condition and previous hiking experience is a plus. It's best to bring your own sturdy hiking boots, although these and other compulsory equipment (such helmet and head torch) are available for rent as well. Be sure not to wear your newest clothes and shoes, since you will inevitably become very dusty and sandy during the hike (especially during descent).
The island has little to offer besides its famous volcano (which for me was a lifetime experience!), but it definitely is worthwhile staying for several more days to enjoy the island's atmosphere, the beautiful nature, the nice weather and the good Italian food.
The island can only be reached by boat, which is a small risk: in my case, due to strong winds and rough seas (which happens rarely) I wasn't able to reach the island on the planned date and time. But of course the weather is not something the hostess is responsible for!
The best time for travelling to Stromboli in my opinion is spring low season, considering the limited amount of tourists and at the same time the comfortably warm weather conditions (not as scorching hot as in mid summer).
In conclusion, would definitely recommend visiting Stromboli and staying with Sigrid; in fact I would love to return there very soon.