Her Bunny Mech is just a jobber, her "berserk mode" is mainly played for gags, and she never uses it when it really matters. Although her being a medic is important, how often does that skill come up? I forgot she was even a medic. As for her being a grim reaper, cameos and crossovers are noncanon and cannot be taken seriously.
Numbuh 3 is the least useful member of sector V and that's an undeniable fact.