How long have you got before this becomes an emergency? I'm wondering whether leaving the catflap on In Only, then all the humans going out for the day, might do the trick. You could leave a delicious, strong-smelling plate of her favourite food just inside the cat flap; fresh meat or fish maybe. She might feel less suspicious about nipping inside if nobody was around and you all seemed to have lost interest in her movements.

Interesting idea about a cat charmer, but it's hard to imagine the cat would come to anyone else if she won't come to you, unless there was magic going on. Do keep us posted if you find someone!