Buying a bark collar for a puppy is a rather controversial decision and one that you should make only after a lot of research.  One option is to simply buy bark collars for small dogs.  This may help you with the size of the dog's neck but it doesn't really address the issue of whether a puppy should have a puppy bark collar or not.

You should first try to identify why your puppy is barking.  Your puppy may be scared, bored, threatened or any other number of things to cause her to bark.  Just know that there are plenty of useful puppy training tips to help control the barking without resorting to a bark collar.

If you find that a bark collar is necessary just realize that there are more humane collars than those that shock the puppy.  There are some that make a noise, a sonic bark control collar, and others that spray a water or citronella mist.