i used to tell my daughter that's "it's painful.. pls dont bite mummy..." she seems to understand and seldom bites.. but some friends shared that squeezing their noses help to get them to unlatch as they're unable to breathe properly. or flicking their cheeks when they bite....
Immediately unlatch her by placing your little finger in to break the suction and tell her firmly "no biting". Other methods are listed here: http://sg.theasianparent.com/the-biting-price-of-breast-milk/
ive tried the nose pinching method and it works for us! just don't attempt to pull yr nips out of baby... cos you'll be at the losing end of things! :P
thanks