Is this the right breed for her?

Today my grandma and I were at the flea market and we saw some German Shepherds for sale. There were 8 of them and the owners were Amish. I felt they were very serious about their dogs. As my grandmother discussed price ($500-$700), I asked about socialization. They are like family to them apparently, and they grew up around horses and sheep and cats and all that good shit, which is important because my grandma has cats. 4 of them. Dogs have been around the cats, because my grandmother's friends have dogs they bring over occasionally.

But, why does my grandmother want a dog?
Recently my grandma was diagnosed with breast cancer. She loses her balance occasionally and she wants a dog that can help her up, so a big, strong dog is necessary (BTW, the Germies are from the work line). My grandma currently lives in a two bedroom apartment but is soon moving into a 2 bedroom 1 story house with partial fencing, but HUD is going to go in and fix it up and make it completely fenced in. The backyard is approx. 30 feet by 40 feet in diameter and has a smaller, broken up shed a few inches off the ground that we can easily convert into shelter for him/her. There is a hole in the side of it so all we have to do is cut out a bigger hole in the side and wallah.

I know this is an active breed, but the house is walking distance away from me and my 2 cousins. I plan on giving it about 1 walk and a run in the nearby fields along with my Boston Terrier Reni daily, and weekly, again with my dog Reni, to the dog park to run around and be free, etc. Here in Michigan we have warmer summers and colder winters, so we can get it a pool so (s)he keeps cool and they will be fine in winter.

Sorry this is kind of rambling on, but I want to make sure my grandma makes the right decision. Thank you for reading.