Well I do not know what locusts your feeding but mine are as a jumpy as anything
. Now I do agree that they are easier to catch than crix but the odd one does escape as they can jump away from you pretty quick and off under a unit wher they cannot be caught. It may depend on where they are kept and what temps they are kept at. All my livefood is kept in my reptile room which never gets below 80f so they are always warm and lively. You can of course keep them slower by storing in a cool room.
But I would bet that eventually your girlfriend would soon get over her phobia the more she sees them.