If you're thinking about a service dog, we don't usually let these dogs run off leash, even in their off duty time, and Goldens, like other sporting dogs do best with off leash run time. Small dogs such as Papillons make great little service dogs for certain tasks such as hearing alert. read more
If, on the other hand, your friend is just looking for companionship, the smaller the dog the better. Big dogs (unless very well trained) can be way too hard to manage for someone in a wheelchair. And that's just for walking. read more