Where do you draw the line?

Roommates can be catalysts for personal growth, as differences in habits may cause conflicts that aren't particularly easy to solve. In this case, OP's roommate was an old friend from college who had nowhere to stay, so OP initially welcomed her with open arms. Shortly after moving in, this roommate, who we'll call Karen, began to trash OP's home, berate her, and cause a general series of uncomfortable scenes that made OP realize that she had to kick Karen out. Things got progressively worse, a…