I use a funnel to get the fruit flies into the dusting jar, especially if the container they are coming from is wider than the receiving container. I do shake, sometimes violently, the reciving jar and funnel to prevent the fruit flies from climbing out. Once they hit the dust, it becomes very difficult for them to climb upwards.

If fruit flies manage to get away from you, I find they usually walk right back to the culture and try to get back in, which they can't obviously. Let your mom know that they are flightless.