Background Pony #29EF
Well, I bet it was anothe roomy that reassembled Amethyst Star because the unnamed pony’s mane and tail color were lighter than Amethyst Star. So I would agree that it was just the unnamed pony because her cutie Mark is a G-clef and not three diamonds. So I would agree that both Amethyst Star and the unnamed pony were present at the Friendship Festival before it was ruined, or sabotaged, or crashed, or disrupted, or interrupted by the Storm King and his troops and later resume after the Storm King’s demise, his army’s defeat, and the restoration of Equestria. So I believed that it was just an unnamed pony that reassembled Amethyst Star with a G-clef—S05E13 Unnamed Earth Mare #1—cutie mark attending the Festival of Friendship in Canterlot and during the song, “Rainbow” by Songbird Serenade/Sia.