So, whining runs in the family too, does it? Two of Edie's nicknames are "whiny b****" and (my new favourite) "needy Edie". She also tends to look morose. Neither the whining nor the morose expression have much to do with how much pain her arthritic shoulder is causing. She also tends not to limp.
The best cues to the amount of pain seem to be whether she: puts her full weight on it when she stands; wants to chase her ball during play time; flips out and races around the yard every few days; gritches at her sisters if they step too close to her when she's lying down; or hangs out in an empty crate. It was the behavioural stuff (the crate use and the gritching) that first tipped me off that she was in pain. That and the look in her eyes which I first noticed in a photograph.
I think if she seems playful and happy with life, you're probably doing a good job with pain management.