By snap I meant jump up etc, sorry if that is not your understanding of the word but it is mine.
http
/www.thefreedictionary.com/snap
http
/www.thefreedictionary.com/nip
From Barbara Woodhouse to Victoria Stillwell, Bill Koehler to Jean Donaldson, any training method I have experienced refers to snapping & nipping as just that; aggression issues. Your understanding of the word is one that I have yet to hear of, though I may be mistaken and will look into it further. If you use words in a manner that are not of common definition without stating so expect to be misunderstood.
Your definition of snappy is of dogs that jump up, how do you define nippy? You state that all small dogs you’ve ever encountered are a lot more snappy, a lot more nippy, and a lot more aggressive. Dogs who have these issues, if you go by the common definition of these words, should never be bred. I went by the most common definitions, ones used by dog trainers & breeders for decades.
They are protective of her because she's on crutches.
I’m sorry to hear your friend is on crutches, but the dogs in her charge only behave this way because it is allowed or encouraged. Dogs do not realize crutches are any sort of weakness that they have to cover for unless they are taught that. There are service dogs at work daily for people with disabilities, many much more severe than crutches, and do not exhibit these tendencies. That is because they were trained not to.
Excellent link, and a perfect example of why smaller dogs should not be trained any differently than larger dogs. The only place I recall seeing badly behaved dogs is when going to the vet. I’ll bet that the aggressive leash pulling poorly trained & usually dominant dogs regardless of size are seen there more often because they have to be taken out & to the vet. They aren’t taken out for fun because they are no fun outside with the unresolved issues.
Perhaps this is why I see for the most part well behaved dogs around the neighborhood. The worst I see is larger dogs that pull like they want to remove an arm, usually walked by younger kids, guess the parents don’t want to risk a rotator cuff injury.
The arrangements by you for determination of an aggressive dog should be applied equally from the tiniest dog to the largest, it sounds like they go through a quite lengthy evaluation process. Many areas, including my own, will allow a person with little or no training to make this decision. I wonder if this is common in other areas, and if they do let smaller dogs with these issues slide where larger ones would be judged more harshly.