I talked about this with friends on the radio show I do, and they said to, instead of having her "sit," and "stay," work on Heel instead, and make "heel" such a fun thing that she'll be interested in that, instead of the other dog. It is important, of course, that you are calm, and very consistent, and if she snaps at another dog, or backs away, you need to correct her, and bring her focus back to you with a command. She's a Dobe, so whip-smart and growing, so getting this behavior corrected now is important! If you need to, you may try a muzzle when you are at the dog park, just to be sure she cannot do any damage to anyone else, but for now, try "heel" and making that fun, refocus her on you, and see how that goes. Remember, Momma Dog will cuff a misbehaving pup, I'll never forget or Saint Bernard, who never had pups of her own, pinning down a friend's puppy who was being obnoxious and giving him a low growl. The next time he tried it, she swung with one paw, and he rolled like a bowling ball across the lawn, but didn't attack her again!

And one of the hosts said to tell you she looooooves England, and finds it very doggie friendly!