Her neck measures 17", while the HS prong is a 23". She's still a puppy and I think that sizing is a little big.
Prong collars are very adjustable.
Please don't give a correction with a head collar. It produces great strain on the dog's neck. IMO, if you are going to be giving corrections, you should use a tool meant for the job.
When a dog saves the life of a man, it becomes clear that partnership knows no bounds.
Fama - T.E.D.D. OEF XI-XII (GSD)(RET)
Marshall - T.E.D.D. OEF XII-XIII (Lab)(SF EDD)
Lucian - Med Alert / Mobility SD (Cane Corso)
Pud - the old man (Pit x Lab)