[m21sniper]

Next time you're at the range, hand her an unloaded weapon and tell her it's hot.

Watch the muzzle closely as she "fires".

If she is flinching it will be obvious. What you're describing typically comes from flinching. At 3 yards it would typically be severe flinching.

If you determine that's what it is, tell her to squeeze the trigger super slowly. So slowly that the moment the weapon discharges she will be surprised. Flinch is caused by anticipation. If you are surprised when the weapon fires your flinch will be after the fact.