A Tiki Arena Build - Refinement and B slot?

quick riposte and renewal are good options

when chill atk comes out it wouldnt be a bad option either

her best refine depends on how you run her, mixed tanks want res and phys tanks want def. she is also very good against lance and blue tome units so if you ever grab an extra LIke, give her warding breath. dont underestimate her ability to duel blues just because of her color

If you are trying to maximise arena score, you don't want triangle adept. It's worth less than skills such as the breaths.
Quick Riposte works very well as a B slot, leaving the Seal free for Close/Distant Defence. However, if you want to keep QR seal, one of the chill skills could work. Renewal could also be an option.
I would suggest changing the Tiki used to one with +Atk/Def/Res -Spd. She will be getting doubled, so +Hp gives less overall bulk than def/res. +Atk allows her to deal more damage per hit.
For the refinement, go +Def/Res. If you want her to be a mixed tank, res is the best choice. If you want to capitalise on her best attributes, go Def.
Here is my Tiki for reference. She is +Def -Spd, and she is by far the most fun unit I have. Any physical unit deals no damage to her. She can even tank hits from Lucina and other falchion users. Her only real threat is blue mages with high attack.