You mean Erica the plat mage armor? If you want an upgrade from Raichi (gold TP mage armor) and don't have any premium plat+ mage armors, then yeah try your best to get as many SU/CR for her as you can.
On another note, stopped at Furfur level 5 because I'm missing some crucial units for him. The lack of rangers and Metus (or another necromancer) is probably gonna stop me from 3*ing level 5. Not sure if Kokoro and Mikoto are enough to stall him. And I probably need an AW and S.AW Rika too for avoiding those pig demons.