How to build Young Summer Tiki (+Spd - Res)

You could simply go with Fury, as it's simply good for getting into the desperation range and her Spd is further increased.

You could always keep her native Atk/Def Bond, but Fury can work too.

I don't recommend DC with -res. Naga tome has a good chance of OHKO, and she will feel quite thin against mages in general. Therefore, I suggest some A-skill which boosts her speed - swift sparrow, fury, brazen atk/spd, atk/spd bond...no L&D because she would almost certainly getting OHKO'd by Nowi.

If you want player phase, I suggest desperation because I don't like her chances of surviving two counterattacks. That will also be her best chance against Nowi because -res definitely puts her into the edges of Nowi's OHKO territory. Renewal is also ok if you don't mind playing slow. Chill spd is reasonable; I did a study on how fast she needs to be to double even someone like Ayra naturally and with +spd, a flier buff or two, and chill spd she can do it so she can get away without QR. She might prefer her teammate to provide chill spd, though.