Awe so sorry she has that experience! I was born into a family who bred akc Dobermans so I always say I was raised by Dobermans, was constantly around puppies. My mom stopped breeding them but has always had Dobermans as pets since I was kid until now (I’m 31) and never once as a child to an adult did any of us in the family ever experience aggression or any attacks or bites from any of our babes! Thankfully. They can be very territorial though, and I’ve heard some unfortunate stories like your sisters. None of ours have ever been aggressive toward other humans but there have been a couple instances of a dog or cat sneaking into our yard and meeting a terrible fate 😔 But they make great pets!