I'd love it if this was part of her character. She'll just randomly say some cryptic/creepy thing about the future and it'll happen.

She actually seemed much more certain about the future too, now that I think about it. A bit different from Garnet's "It's like a river, you control your destiny." Which is either an oversight or Sapphire's less perceptive with Ruby attached.

Or more self defeatist.

"It is all just going to happen. Nothing I can do about it"

"SCREW THAT! I am going to give destiny a wedgie in the middle of the school assembly and then take you out behind the bleachers, GURRL!"