User blog comment:GenericUser987350135/Archwitch Deck Guide/@comment-25027477-20140622175125/@comment-25007009-20140622191635

"Attack has a much larger impact on cards than defense. Due to this, it's generally better to max the attack of all of your offensive cards before looking at defense. An exception to this is for 0* SR 200% AoE buffers that are dying in 1 hit, as 10-20 defense arcana can help them live for an extra round."

If she's an SR rather than an HSR, no. If you have nothing else to spend medals on, yes. If you have already maxed the attack of your offensive cards, yes.