Or one of her by-now-aged girlfriends last seen in the video?

@Otokichi786 said:

Or one of her by-now-aged girlfriends last seen in the video?

Possibly.

I always thought it's her younger self.

@Q4428 said:

I always thought iT's her younger self.

Hmm, I have to re-watch. If I remember correctly doesn't she do a cheer for herself in the video? But I always thought she was just trying to elevate her self-esteem. However, it could be she was sending her future self a message.