I visited Anise's cabin shortly after finishing Bleak Falls Barrow. Later on in the game, when I returned to riverwood, I was assaulted by three thugs. I had not killed Anise, so I figured they were from Sven, the local bard and *&%$%hole. Since I had completed the quest to allow Faendal to follow me around, I had expected this. Once I killed them, however, I noticed the note said it was from Anise. I do not believe I have done anything to antagonize her (apart from ransacking her house, minus the basement)