Bridal Tharja build

If she's +spd then I recommend to have her go with a Bladetome build but otherwise stick with her default build and change her B skill to something you think will work on her.
Give her +atk or +spd seal.

I don't think that you should run enemy phase skills (such as QR or close counter) as her defenses are really low, being a 21/21 defensive spread. Building her attack and speed as much as possible would be the most beneficial for her, so L&D, Swift Sparrow, or her native Atk/Spd bond with her personal tome would maximize her amazing 35/35 offensive spread.

B skill should be desperation as usual for mages, or could be a chill skill or the new Spd Feint if you want to debuff.

C skill is flexible, should probably be a threaten or buff skill.

Seal should be either Spd 3 or Atk 3, whichever matters most to you. Possibly heavy blade.

The special should be moonbow or glimmer as always. With heavy blade, you also have the option of draconic aura, as it will proc if she attacks, gets counterattacked, and doubles her opponent. Of course, you could still run moonbow/glimmer with heavy blade to proc a special on enemies that can't counterattack.

Hope I helped!