If he was really scared of them and they kept going off in the neighborhood the whole thing is spawned from a legitimate fear....which is hard to dismiss as a mommy. In any event, she probably does need to just put him in his room and do some sleep training so that he can gradually get used to his own bed again. Maybe a nightlight and promising to check on him in 5 minutes, then 10 minutes, then when she goes to bed.
Recently I've been telling my 2 year old who tries to stall bedtime and keep me in her room that I have a lot of mommy things I have to do before bed--the dishes, vacuuming, clean up toys, etc. and that then I need to put my pajamas on and go to sleep b/c I am so tired and she's let me leave the room. Maybe she can tell him she has to do laundry or something equally boring and that she'll come check on him when she is done?
But if I was her I'd work on getting him back into his own room.