I had to use a pinch on one of my Dobe's from a young age, but was able to train off of it rather quickly. I usually don't recommend it for puppies, but in certain cases young dogs do benefit from the correct use of a prong. My current puppy is awesome in a flat collar or nylon slip lead. But not all puppies are as easy...I got really lucky.
I haven't seen your dog or you working with her, so I can't say if it is good in your situation or not. I know my training club supported the use of a prong on mine, which helped. Some people put a bandana on their dog so people can't see the prong and judge them. I sometimes get comments when my Dobes are puppies and their ears are up in posts, but I never care or say something like, yeah, it really bothers them, just look at them (as the puppies are happily wanting some attention or petting), or depending on my time let the individuals know it really isn't that bad, etc.
I used the prong just long enough so that I could train and have some decent focus from a prey driven wild easily excitable monster, without the dog choking to death and being a sled dog and pulling my arm off.
I know some of the people at the training club use head halters for their dogs (not Dobes), but I also worry about using them with Dobes for the reasons people already gave. Some even put puppies on harnesses, which does encourage pulling IMO but doesn’t hurt the neck when they do pull. It works good for some. I even know of one that uses a metal choke for her Dobe puppy, but I would NEVER EVER recommend a puppy who likes to pull be put on a metal choke to be trained, it can really do damage to the puppy.
Jessica is TOTALLY right, the walk is whatever you want to make it. If you want the dog to heel and stay beside you during the walk, then the dog should heel at all times, you can train her to do that easily with a slip lead for walks.
For a competitive heel ( I don't know if you are interested in getting a CD or higher), I train off leash, no collars, armed with lots of treats and toys in my house or backyard. I keep the sessions short and happy and it works really well and go longer between treating as I see they are connecting the dots. My first Dobe I trained competitively heeled better off leash than on b/c of this in the beginning and for some months after. My current Dobe is doing awesome at both, but has mostly been trained naked with treats or toys so off leash and on leash look the same. But training a walk and training for trials is different, but the concept of heel is the same, heel means walk beside me in heel position, loose leash or no leash.
If you want to interchange between heeling and "go free" (giving freedom) then do so. Say she walks in a nice heel for a little bit, then you let her lead and "do her thing" for awhile, then call her back to heel, and so on.
If all you want a nice loose lead walk, then train for that. You can do a search in this forum for more detailed info ( I searched but couldn’t find the thread quickly), but you can use treats to help her learn this. Treat her for paying attention to you and walking correctly, use praise and let her know when she is doing well.
The make like a tree (stop walking when you feel pulling) can work for some dogs, but not all. Also you can try changing directions real fast when she is getting too far ahead of you, that will make her have to stay somewhat close to you or at least keep an eye on you so she can keep up. Some dogs think it is a fun game, and it is effective for some.
Ask your trainer what else she or he recommends. Also ask the rescue, I am sure they have dealt with their fair share sled dog Dobes. She is still very young though, and I do think it is important to keep that in mind.