My exact thought!!! A Fila fits all the criteria you have, and more!
Are Filas the type to welcome other dogs onto the property? She mentioned wanting a dog that is not prone to having "issues" with other dogs or other people...kids playing with her kids. Are they apt to be highly suspicious of unfamiliar kids wrestling or running around with the family kids? Or not more than lots of other breeds?
Most dogs that were bred to guard something, I would think would be prone to some degree of suspicion of any novel, living thing coming onto the property...some more than others....not only by breed, but by individual. In fact, most dogs, regardless of breed will have some degree of suspicion of strangers coming around their place.
My GSD that we had when my kids were toddlers was wonderful with not only my kids, but their friends and even strangers that came around. If the stranger was friendly and seemed to have business at my house....workman coming to do something, delivery people, meter readers or whatever, he was great. He just watched and was very relaxed. When someone tried jimmying the door late one night, he knew that was a no no and went balistic at the front door. He was not dog aggressive, once he got neutered. (he was before)
Anyhow...that Marm sounds pretty nice. It's great that you're looking into it way ahead of time so you have plenty of time to go meet some, talk to people etc. From what I understand, which isn't that much, the best livestock guardian breeds....the ones that really take care of their flocks are raised with the livestock from a VERY early age....(3-4 weeks) They live with the sheep or whatever out in the barn and have minimal interaction with humans. But maybe you won't need that degree of "work ethic." When you talk to people with real, working dogs, you'll find out more.