should I build this f corrin or wait

I love mine and its +defence -attack. she is the debuff queen with 47 defence on initiation combined with dark breath and seal res as a B skill.

Corrin's resistance isn't all that great to begin with. Even with a Resistance boon, it's only 24, which could be enhanced with skills, but, in my opinion, not worth the trouble. Corrin excels in speed and defense, and she can debuff if you're keeping her default breath, or you can do what everyone else does and give her Lightning Breath+ and enhance her defense or speed even further with a refinement.

Either way, I'd keep her.