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)
If you stole an item from someone, even if they didn't see you do it, the thugs can be sent after you anyway. Therefore, if you grabbed all the items in the cabin while she was still alive, then they counted as stolen for some reason, and she can even send the thugs from the grave if you did kill her.
I didn't know she was "evil", because she ain't never did anything wrong to me. I've always enjoyed beheading her, whenever I drop by her shack, but I killed her for the fuck of it, just like I do with most good people I bump into. The fact is that I really enjoy murdering and butchering people for the fuck of it, but it would be funnier if she was really a good old lady.