Private First Class is an Army rank, not a Navy rate. However, there are 4 Navy rates at the comparable E-3 pay grade: Seaman, Fireman, Airman and Constructionman. There are specific coins for each rate, each with room on the back for engraving.
Tell me your daughter's rate (pay grade) and what rating (job) she is going to A school for and I can point you to the right coin. And if you don't know, you can fall back on the Ship 12 coin.Or the RTC coinYou can find them and many others at pirgifts.com.
Hope this helps.