If you can't deflect the force out of the way, then deflect yourself away from the force.
Don't extend the usual Wing Chun guarding hands when dealing with a knife attack. Your hands will get slashed. Instead, use your body to evade the slash.
Always hit into the center line of the opponent.
Slowly creep up to the opponent until you can use the gliding step to charge into the opponent. Charge in when the opponent has made a mistake, when he is caught off guard or is in between techniques. There is no easy way for a smaller woman to charge into a larger man. Use counter-attacking instead.
You don't always have to find an opening to hit. Just hit anything that sticks out or is close.
Against a sudden sidekick to your stomach, apply a shift and double low Chum sau. Sometimes you have no time to evade the force completely by stepping.
The Wing Chun Kung Fu Digital Library