I had two for about 11 years...
I lost both of them last year to old age & cancer issues
Anyways, they were awesome! I treated them like family. They were spoiled and they were house dogs. They were great around people and kids. The male was a bit TOO happy around people, he had a jumping & slobbering problem that got better in time.
They have the potential to be dangerous dogs if their temperment is bad. If you can meet the dog's siblings or parents that's a great thing, if not, spend some time around her and see what she's like. Does she tolerate hugs, tugs, etc... My female loved it.
The only thing I didn't care for as an owner of Rotties was people's generalizations of them as junk yard killers, and the SHEDDING the damm hair gets everywhere lol...If you keep a clean house and vacuum often no biggie, if not you'll want to pickup that habit.
Honestly right now I don't want dogs again for a while, I want to travel and not worry if a hotel takes dogs, dogsitters for when they don't, etc... When I do get another dog I might consider going with a Rott again but then again it would just remind me of my two babies so I might go for another breed. Still kinda tears me up thinking about them, I'm sappy that way.
Ok, after all that rambling...bottom line is they are great dogs. Treat them well and it will pay off. If you want a dog you can throw in the yard and leave there, please don't adopt her.
Oh, one last thing, they are stubborn as hell, so be prepared to spend a little time in training. It's fun and they love it.