Why is my 1.5-year-old Rottweiler suddenly aggressive to dogs and people?

Unfortunately, it's relatively common for behavior issues like this to develop between 1 and 2 years of age - this is the period when dogs reach social maturity. Often, they may have been fearful or nervous about many things when they were puppies, but don't start to act out aggressively until they are a bit older.

Aggressive behavior in a large dog like this can be a serious problem, and is best treated by a professional who can work with you and Molly in person. I would recommend making an appointment with a veterinary behaviorist who can evaluate her and put together a treatment plan to work on the problem. You can search for a board-certified veterinary behaviorist here: www.dacvb.org

In the meantime, I would recommend keeping her away from people and dogs as much as possible for safety reasons, and to avoid making the problem worse. Treatment for this problem is generally based on teaching the dog to associate good things (such as treats) with seeing people or other dogs, starting at a distance where they are comfortable and gradually working close from there. The behaviorist can help you with this, since it can be hard to do on your own!

Punishment of any kind for this behavior (including verbal scolding, leash corrections, shock collar corrections, etc.) is not recommended, as it tends to make the dog more fearful and has a high risk of worsening the aggression over time.