IMO, if you can train your dog to walk to heel using positive, reward-based training, why choose to go any other way? Rattling keys is different from something like a shock collar, but I agree with Top Barks; does the key rattling make her walk to heel because she doesn't like it and wants it to stop?
I have no experience of working dogs, so you may choose to ignore the above, but if it is possible to train them without using aversive training (which it must be, as Helen's comment makes clear) then I would choose something positive and reward based every single time.
More 'traditional' (not sure if that's the right word to use) forms of training might work quickly, but that doesn't mean they are necessarily the best.