You don't use Infantry at all?
In that case, foddering her off is the logical option aside from keeping her for HM.
Death Blow 4 is good on Brave units, like Reinhardt. Someone that can either quad because of high speed (like Setsuna) or someone with a speed stat that you don't care to increase (like Gordin).
You can also give it to Desperation units. If you have a way to buff their speed, like with Waves, Tactics, etc, then DB 4 can be a nice option for more power.