She rented the house from Airbnb. Private individuals rent whole apartments, houses or rooms in their house to essentially strangers using the service. For example, this is an example of an entire house for rent in Wrigleyville.
While I was first thinking that this seemed like a risky move, the party turned out very well. The house was beautiful, with a nice TV, stereo, fully stocked kitchen, and even a decorated Christmas tree. Since the house was so nice, everyone seemed to go the extra mile to keep it clean - if a drink was spilled, someone cleaned it up right away (probably the fact that there was a damage deposit helped, too).
A recent BBC News article on Airbnb described the phenomenal growth of the service and how an idea that seemed radical (renting out your home to complete strangers) is now becoming mainstream.
Airbnb is a website matching up homeowners with tourists and backpackers wanting a place to stay. Set up in 2008, it's one of a wave of sites - like Wimdu, and Homestay - making money out of those seeking a bargain. The firm says it has listings in more than 35,000 cities in 192 countries.I know of other people who travel around the world using Couchsurfing, where you basically just crash for free on a strangers' couch. This seems even stranger, but apparently works out well and people generally make friends and have a good time, although of course there are horror stories (probably the ones your mother would send you if you told her this is how you planned to travel the world).
Likely one element that makes this successful is the fact that most of the people doing the hosting and the people using the service are outgoing and friendly types. The sort of person that would use or trust someone else in the first place are generally the ones that would make these services successful. Another type of service like this is HomeExchange, where you can exchange your home in a tourist friendly area for one in another tempting locale (generally there are additional checks on these sorts of arrangements that you wouldn't see in Couchsurfing).
An analogous situation is when we go on a tour with a company called "Backroads" where you travel to great locations like Italy but you do active vacations including bikes, hiking and even kayaking (although I am certain it wouldn't stress out Dan). If you take an "active" tour, you seem to have positive experiences with your peers, since the fact that they volunteered for a tour involving physical fitness (and not just sitting on a bus) makes them the type of people less likely to complain and generally to have an upbeat attitude. We have been on four of these trips and have not had significant issues with any of our fellow tourists, even though we are confined with them (at various times) for 5-7 days.
The idea is that the type of people likely to assume that the other person won't steal or take advantage of you, and in fact might be someone interesting that you might enjoy spending time with, is a positive social trait that would be associated with many parts of the world. I don't know if I'd expect this type of reciprocity everywhere, however.
Cross posted at Chicago Boyz