Is their old house is nearby? Ask the new owners if you can go round and maybe call your cat or tap her food bowl with a spoon. Cats can sometimes find their way back home even from fairly large distances.
I am so relieved for your friend - the cat is probably confused by the move - might be worth trying to keep it indoors for a couple of days until it feels the new house is indeed its new home.
Cats are like that, though - so glad this is a happy ending!