Need some help with a build!

The upcoming TT has a darting stance, which might be good for her along with her base A skill.
If you don't care about atk, then fortress res plus wings of mercy are pretty great.

Edit: IGNORE ME!!!

Honestly, her kit is already awesome straight out of the box. Her Armour March and Vengeful Fighter makes her a strong mixed phased unit especially in armour teams.

Her A skill is the only thing that desperately needs replacement: Distant Counter, Close Defence or even Sturdy Blow will do wonders for her and it obviously depends on how much you are willing to invest into her. Vengeful Fighter is a great B skill but if you have a spare Brave Ephraim then you could also fodder off Special Fighter, essentially making her a Red Brave Ephraim (with a guaranteed follow up based on her Defence). Armour March is again fine as it is if you are planning to use her on an Armour team but anything from Tactic skills to Wave skills can really help her if you want to put her in a mixed team.

Bonfire is great with a guaranteed 22 extra damage on trigger. Alternatives include Ignis (better with Special Fighter) or Aether (duh). Assist skill can be anything but i recommend Pivot to get her into the fray quickly.