You don't say how long she is left during the day or does she do it while you are there? If she is left a long time on her own then that is your answer, dogs shouldn't really be left on their own for more than 4 hours at a time, if you don't leave her for longer than this then a good solution is to buy her a dog crate, an hour a day isn't too bad though a Rottweiller could really do with double that amount or at least an extra half an hour split between 2 walks 1 in the morning and another in the afternoon, I keep German Shepherds and I also have a Border Collie (4 dogs in all) and they go out for half an hour at around 6-7 in the morning, and then they go out for 1-2 hours in the afternoon usually around 2.30, and most of their exercise is off lead, if I didn't do this they would get bored and eat everything in sight, I also take them out extra in between these times and take a couple of balls and those ball throwers or a Frisbee, for a while in a field close to my home, you really need to keep these breeds of dog occupied or they will be destructive! I'm not knocking you for rescuing a dog in need, but if you are unable to give her the time, may be a less active breed might have been better?