Cecilia

I have the same +atk/-spd. I alternate between standard Gronnraven+build, particularly when I'm running her on an offense-heavy team and need someone who can soak a few blue/colorless blows, ideally for arena offense. If running another tank, Gronnblade also works with those IVs as a powerful one-shot nuke, equip her with something like Fury or Deathblow. If you're trying for Sigurd, he'll be a natural partner for her if you equip him with Hone Cavs.

It's cheesy, but GTBreaker Gronnblade+ works phenomenally alongside Rein/Lyn, I've had plenty of deathless streaks ended that way as I often rely on a green mage to tank Rein and possibly Lyn as well.

I don't think Cecilia has any options out of those two, but generally +atk is the only IV that really matters, and she's only desirable alongside other horsies.