How old is she?
Why did the trainer recommend a choke collar?
One of the very best websites on dealing with puppies is Dr. Ian Dunbar's Dog Star Daily. Tons of videos and free downloads with a wealth of info, like this one on leash walking: http://www.dogstardaily.com/files/WalkingOnLeash_1.pdf
Not sure if you have to create an account to access all the videos, but it's free and totally worth doing.