[Fosavoa]

I hate to be the turd in the punch bowl here, but Sai's new behaviour could be a fear induced defensive reaction. She may have figured out cowering & looking for reassurance doesn't make what she perceives as a "threat" go away fast enough, so maybe a big ol' threat display will. I doubt this was true courage. I could be totally wrong, but it sounds more like a fear-induced bluff to me. Dogs who are bluffing can display both defensive & offensive body postures. Some will use even use displays like many mentioned by the OP - stiff front legs, ears foward & advancing toward the "threat." This is done to make themselves appear bigger & badder & make the "threat" go away. Kind of like the frightened cat who puffs up all his hair & sidles up on a threat for example. I myself would consider it much more of a breakthrough if Sai would have reacted in a calm & collected manner. Defensive aggression/fear aggression is not good & can end up in a lawsuit.

JMHO.

Blessings ...