+hp -def legendary lucina

I would say, keep her swift sparrow, or go with fury.
Her weapon gives her +3 Speed, as does the weapon effect give her +4 to all stats whenn she fights against melee units.
There are many units out there who have some kind of distant counter effect, so i think it is a good idea to preserve her defensive stats.
With her HP boon she has her bulk up's quite a bit.
With her weapon effect enemys need 66 physical/64 magic attack to 1-shot her.
An with her weapon effect(s)+ swift sparrow she reaches 46 speeds,so no worries about "not the greatest speed".

You could use the Desperation, as it is just a good ability,or if you want to be a bit more creative you can use things like "Atk/Def Link" or "Def Feint" as they work exellent with lucinas "Future vision".