In the gift of time this artifact is left in a locker on ESM for Carston Hawthorn by his time-traveling great grandfather. it has pictures painted on it which he thinks are a sort of a map or clues for how to stop Gaia or prevent it from being created.
That guitar was not the one she actually plays in the Savior of HomeWard story,
Guitar playing was popular on the LDS homeward colony Due to Emily's playing and teaching others to play.