Zillow likely has a clause in their contracts with MLS/wherever else they get these pictures, that they cant allow the pics to be used for any other purpose other than for posting on Zillow. They are trying to enforce this since they have apparently gotten dinged by suppliers in the past. Since they found a blog that explicitly stated "i got these pics from Zillow," they had a lawyer who had apparently been working there ~1 month send out a standard C&D letter, even though the facts didnt exactly fit (when all you have is a hammer, everything looks like a nail, etc.). It obviously became a PR disaster for them but could also have just gone the opposite way where a no name blog using their pics stopped doing it. It was obviously a mistake but I'm sure there was no malice on their part, the rash of people rushing to condemn them for stifling free speech are being silly. It was a standard process thing that didnt quite fit and got blown out of proportion, i'm sure everyone has encountered some form of it in their job before.

All she has/had to do was take out that statement that 'it's from Zillow' and the problem goes away, Zillow doesnt care where you get pics from as long as they have no liability.