My vision of Nesa is that above all else, she is extremely competent at her job. It may not be the job she trained for, but she decided she was going to do her best at it. Then she got to know people, and developed loyalties - one of which was to Sephiroth. She can't match him in physical combat skills, but she has a black belt in administrative judo, and she also has a rather fierce protective instinct when she's roused.
Heidegger's staff won't know what hit them - or rather they will (it'll be all the paperwork they sent over, on the return trajectory), but they may not recognise why it hit them that hard.