I can think of two ways of tackling this but I am sure there are other ways too. And absolutely don't use negative responses! You are so right there! Not just with tricks but any time you are training.
My first inclination would be to teach her some impulse control starting out like this:
I'm sure you will have a more exciting first few attempts! But it is teaching the dog to work for the food by controlling it's impulse to dive for it. You can also work with food in your closed hand and reward for the dog keeping a little distance from your hand, then once the dog has got this you start opening your hand a little but still guarding the treat so the dog is not rewarded for snatching. Or you can simply teach your dog what luring is by having a luring lesson - you click and treat when your dog is a bit calmer and shape following your hand nicely for the treat.
The other method is to teach your dog to hand target. Just let your dog touch your hand with her nose and instantly click and treat. After a few attempts move your hand so your dog is turning her head to touch it, then moving a pace to touch it, then before you know it she'll probably be following your hand. Just make sure you keep the rate of reinforcement and praise really high for her - at least once every few seconds. My dog follows my hands whether they contain treats or not because he knows that he will be rewarded for it. You can also train your dog to follow a target stick.
Why do you think she loses interest in free shaping so fast?