She said that her grandson aged 4 was having regular nightmares, so just before he went to sleep at night the mother asked him to think of 5 really enjoyable things that had happened. She would cup her hands and he would say the 5 things into her hands. She then pretended to mix them up in her hands and then sprinkled them over his head. Since then he has had no nightmares.
The reason we were talking about it is because my DS (6 years old) was telling her that he had had a bad dream the night. So that evening we did the same technique (and for a couple of days since) and he has had no bad dreams since then.
I can't guarantee this would work for your kid, but it might be worth a try!