This is my -HP +Atk Faye, good enough?

Pretty good. Her Spd is lacking, but she's good outside of it.

I don't think Glacies is really the special you want here. 26 res isn't really enough to justify using it over Luna or Moonbow.

I'm not really a fan of combining poison strike with life and death (or honestly, using poison strike at all ever). Poison strike is something I figure you'd want on a unit that is lacking in the ability to finish off enemies in one round but tough enough to reliably survive counterattacks and/or the enemy phase.

Tbh her default weapon with either atk smoke, savage blow or poison strike would be better on her.

The weapon CAN work. But she needs heavy spd suport

I have a friend with a +10 Faye. He runs Guard Bow. I think Gratia is a good bow for certain situations, but Life and Death and Poison Strike don't seem to fit on that Faye. I'd try Distant Defense 3 and Quick Riposte 3, along with a Def/Res refine on Gratia, with Distant Defense seal. I think you'd be more pleased with your results.

Don't really see anything that synergizes.

-Gratia is okay. It neutralizes bonus from ranged units.

-Rally Def/Res is okay for Arena, I guess, but a mobility skill is probably better, depending on team composition.

-Glacies will need to be replaced. Doesn't make sense, at least for me, to run Glacies on a unit that only has 26 resistance.

-Poison Strike is a bit odd and doesn't really flow well with the rest of her kit. Might want to change it, at least in my opinion.

-Spd Smoke 3 is a good skill, but wouldn't it be better used on a unit that would be more into the mix, like a tank? Seems kinda wasted on a unit that's so frail.

-Speed +3 is one I'm not entirely sure of since even with said seal, her speed is kinda low, and she won't be doubling that many units compared to if she didn't have it.

I think the current set seems more like a "Jack of all Trades, Master of None" kinda build. but even then her defenses are seriously lacking, to the point to where I don't really know how she'd survive a hit from a ranged unit.