A knowledgeable member with military experience related that supply is an exception to any usual duty formats.Wasn't 4/22 her day off? A person is not required to "report" on their day off. She would have been reported as "day off" by her platoon leadership in the morning.
Ranking soldiers in supply, even if of low rank, can summon anybody in the unit at any time to account for a sensitive piece of equipment that they have been issued. That summons carries the same weight as if it were issued the unit commander.
The knowledgeable member also related that supply personnel have this authority because the commander has ultimately signed for every piece of sensitive equipment in the unit.
I suspect that an armorer can also be summoned by a more senior armorer at any time to assist in locating sensitive equipment, say a weapon. This yields a strong possibility that Robinson contacted VG and related that a weapon was unaccounted for.
He then summoned her to help in tracking it down. Or, related that Sgt. "S" had ordered her to be summoned etc. In either case, the victim responds as she is familiar with the summoning ability and knows that weapons are especially sensitive and must be accounted for immediately.