In case of some very wierd problem where BigSister cant detect the status of the game (say some unknown error or else), Bigsister will restart the game if 5 minutes are past without her knowing the status of the game. Also, if for any reason she stops beeing able to reading the game memory (wow crashed or exited) she will also restart. If bigsister detects that your character is not ingame she will restart, she will however properly detect if you are loading something (ie, entering BG) and will wait in that event, if loading takes too long she will also restart.
I hope all of this rules shall be enough to make bigsister able to handle any situation she comes up with... but time will tell.
All of those rules can make bigsister detect an unknown event and restart everything when she shouldnt, those situations should be reported so that i can teach bigsister how to behave in that event (an old bug was when she didnt know that it could be possible to go from in-game to loading, so each time she detected that she thought game had crashed and restarted, so she restarted each time you entered a BG).