Parhelia is an anti demon, and demons are pretty common enemy in aigis(atleast compared to other race like orc/angel) so i think its pretty worth for raising her skill. She is way better than Chloe against demons.
Though, you can always wait for Chloe's revival for Parhelia SU, so feeding her Fes might be a waste.
Its better to save Fes atleast until you find a unit that you always use and you want to SAW her/him ASAP.