Summon tickets are paying off.

Congrats on the pulls. I suggest keeping Ophelia's prf and using desperation. 36 spd is frankly not amazing for an infantry blue mage but it's also not bad at all. However, the same is true of 34 atk; she just becomes a pretty average infantry mage with this interesting tome that accelerates special cooldown, which makes desperation moonbow quite cost-efficient.

If you're pulling any more blues on the banner you might want to wait to build her. If you get any that's not -atk the AoE special build is really the preferred way to go for her. I guess you could still do it on 53 atk after L&D. It should still be a pretty high percentage OHKO against player-built opponents, and with 41 spd you'll double a decent amount in PvE.