Would you not agree that Ann living there does seem rather odd/creepy. I don't know anyone that would live in a place where their friends/relatives they knew had a terrible death.
The Library and Canteen at Colombine high was demolished in after the 1999 massacre also
I think you'll find that there are laws against tearing down Grade "listeds". WHF was the property of a charity who might have had views about it's destruction.
Thinking about it, I probably wouldn't have wanted to move into it immediately, but Ann didn't which MIGHT suggest that some thought was put into it.