Weapon Refinement on Young Tiki

You should almost never refine a weapon with more might because unlike def, res and spd refined weapons atk refined weapons gain only +2 extra might. Like you said, spd is not that important thanks to Quick riposte and it also doesn't help her matchups all that much. +def is the best option because of her weapon type and IVs. If you want to use her as a mage bait then go for the res boost.