i wouldnt put a dog or a puppy on a harness because the dog and pups will have more control over their heads and bodies. people make this mistake all the time and then wonder why they dont have control and their dog isnt good on the lead/harness.

harnesses were originally made for sniffing dogs, as they like having their nose on the ground constantly and when they are on leads, they have linited access to the ground as the collar and lead hold up the head.

you would be better sticking to the collar and lead for your walks to be more of a success. she is still young and you just need to be consistant with her.

hope this helps!