Beautiful girl, and the sweet temperament is not surprising, even for a stray.
Bela, my puppy mill mama, arrived in rescue with one of the sweetest, gentlest temperaments and manners her foster mom had ever seen in a rescue. She wasn't taught anything in her early years, yet understands house training, and walking on a leash. She learned "wait" reliably within about 6 hours. She never snatches food, but takes it from your handle very gently, as if she's trying not to hurt you. She delicately sniffs at you, and tries not to bump against you while she's playing.
Yet, if she wants to, she CAN get tough. I've seen her warn Gracie countless times when Gracie is a little too wild. But she always does so within normal and appropriate doggie manners.
Shelties, as a general rule, are just intuitively polite, I think.
That aside, I really do wish she were closer to me - I'd take her in a split second.