I came across this shot on Rlan's "Secrets of Sonic Team" page.
Amy's position isn't the only thing strange; I personally can't remember Amy ever being able to access or be in Holly Summit, or a situation where she was talking to Knuckles alone.
I'd be grateful if someone could translate what Amy's saying, may shed some light on this mystery.
I don't remember anything about Holly Summit, but she does briefly encounter Knuckles in Central City.
In that screenshot, she's asking him if he's seen Sonic. I don't think that dialogue was ever actually in the game, it's probably just a mock-up shot and not even from a prototype.