The synopsis for an upcoming episode teases May’s discovery of what happened to her, bringing back the young Inhuman girl in an unknown capacity.
[SPOILERS for those not caught up on Agents of S.H.I.E.L.D. ahead.] Back when Agents of S.H.I.E.L.D. first began, the show built up The Cavalry persona that Melinda May (Ming-Na Wen) had around the organization.
This was a day that has haunted her ever since, and will soon be explored again.
Instead of May single handily taking down an entire army, the true event had May watch a young girl kill all of them as a result of her newfound Inhuman abilities.