What should I do with a +spd -res nowi?

I would keep that one. +Spd is one of her best boons, especially at higher merges should you get to that point. -Res and -HP are her 2 best banes so overall i'd say you pulled a good one go ahead and build it.

The -res is gonna hurt a bit, ideally should be +spd -hp if you're going for a spd nowi. but hey, if your team comp covers blue mages you should be fine. (she shouldnt be near greens anyway, and red mages are pretty rare in arena).