I wouldn't use the halti collar on a pup that young. Get a clean paint stick and smear some peanutbutter or that squeeze cheese stuff in a can on the end of it. attach her leash to her collar and let her start licking at the stick. start walking slowly forward. She will be so interested in the stick she will forget about the leash. From time to time take the stick away and she if she still ignores the leash. If she does, give the stick back, if she messes with the leash give her a gentle tug on the collar and say leave it. As soon as she leaves the leash alone, let her lick the stick again.

You can also use the stick in a fenced in area (like your back yard - not a dog park) let her off leash and let her lick the stick. You start walking. When she catches up to you she gets to lick on the stick and lots of praise - she'll learn pretty quickly that it is much more rewarding to walk next to you than to wander away.