I am assuming you mean that they dont like being contacted when contesting the ball?  if so then they need to get a little physical.   I find the best way to get them use to contact and i dont mean playing rough, i mean just fair contest for the ball, and the odd accidental bump and push, is to make drills a win lose situation for players.  one on one, running to get the ball.  the front person will be the one you throw it to, roll it on the ground and the front one gets the ball (this is sometimes best played on the grass as at first they may end up diving onto it...lol), standing side by side and sending a high pass inbetween them and the one who wants it more will get it, and one person holding onto the ball, and the other one tries to take it out of their hands.  it increases that inner aggression you need in a good netballer, and then your job as coach, is to funnel it into their skills so they use to correctly.  

the other drill from defence and attacks, is to flood the circle with defence players, so there is little movement without some kind of contact, and the 2 attack players will also learn to get around players even though there is very little room to do so.  when you take out again all but the 2 defence players, the circle will seem huge, but they will be use to a little contact to get free and the defenders will be use to bumping into players while they are looking for the space to shut down.  you can also add a drill of high passes into the circle (to anyone or no one) while its flooded so they can get use to jumping to get a ball for intercepts, passes, or rebounds.  just make sure you have taught them about correct stance, landing areas, take offs, when to catch vs tip.  by the end they will want the ball so much more than the other team they will be unstoppable. 

hope that helps and you have some fun with it.