Sid, any dog can be just what you want them to be, some have stronger inheritant traits,
I would suggest a medium sized mix/rescue for the elderly woman. They tend not to have as many ailments which results in smaller vet bills, and perhaps as you said, a 1-2 year old house trained dog (35-45lbs).
Pups need excersize and play time, and in turn you get a dog lees prone to chewing distructive behavior.
All of our dogs have always been very protective of of family and home.