Have you considered a Brittany? It sounds like the Brittany may meet a lot of your requirements. They are wonderful, social, loving little dogs. Medium sized with short coats that really don't shed and only require once a week brushing.
They are in the Sporting group and have a lot of energy, but they do just as well as house pets as long as they get some reqular exercise. I think this is true of most breeds though, because total couch potato dogs tend to get fat, and that can generate some health concerns. Brittanys can make a good apartment dog too bause of their size - as long as they do get a chance to be outside for some good tiring play
I love my Brittany so much! He's the most loving and adorable, cuddle bug. He was very easy to train. There are pictures of him at varying ages all over the forum
I am so interested in and attached to this breed now that I can't wait to be able to have another.
Here is a Link I found with some Info
Be sure to read the FAQ - good fast info is there
There are Brittany Rescue Organizations in every state, as well as good Breeders - that would be a good place to get information. and also a Brittany if you wanted to get one.
Good Luck on whatever your sister decides on