Without her spear, yes, it's rng without help from other hime abilities / summon actives. Otherwise, her spear increases her Abi1's burst gain from 20 to 35, which will guarantee PF within the next 2 turns.
Ah ok thanks! I went with her bow as a soul weapon instead, but just found out Osiris has a burst boost so I should be able to guarantee it within 2 turns.