From the Harry Potter book: "Mrs. Dursley was thin and blonde and had nearly twice the usual amount of neck, which came in very useful as she spent so much of her time craning over garden fences, spying on the neighbours." In this case that means that her neck was very very long, and that she used it to be nosy and peer into her neighbor's yards. This is a phrase that you would not normally hear as a description in common speech.

This really makes me wonder who you are talking to! :O :) I can only think this is a more literal way (and maybe not nice way) of saying that the woman in question had a very long neck...

她的脖子是正常人的两倍长。