DC Silvia?

As soon as the datamine came out, I knew looking at her stats and base weapon “she’d be good with Distant Counter.” Lo and behold I free summoned Hector on the Fury banner, and have summoned Silvia tonight with not too many orbs. Unfortunately, she’s -atk.
But she is +spd which is fantastic. I hate to summon for another one when I could end up with inferior IVs after all. But I wanted to build her as a straight-up mage tank and killer. Is 37 atk good enough for that? I could refine her sword to atk to raise that to 39, but I would prefer to refine it to spd so she can survive/kill Nino (both but especially flying who I really have trouble facing in the arena) without G Tomebreaker.