Do it! Mine is +SPD/-RES and I did that a while ago, it was definitely worth it. She kills basically everyone that's infantry. She's also fantastic for carrying training teams in-game. I gave her Death Blow 3, Desperation (& Vantage, just in case), Ardent Sacrifice and Moonbow.
In Arena she kills basically all infantry except Robin-M (unless he's a dodgy iv or build) and some softer cavalry and fliers. Paired with my anti-Hector Olivia, she kills basically all but Robin-M and Knights. Her stat total isn't high but with her Robin-M, Olivia and a L1 bonus character I usually get 3800-4000 which is enough feathers for me. Minerva causes problems though