Well C isn’t necessarily a bad grade, and B is fairly good.
There’s no hate towards her, she’s just ‘pretty good’ in all aspects without really shining anywhere.
Titans; she’s a good backup choice for dark, her mana suppression isn’t amazing but better than nothing.
Raid attack; she’s durable, doesn’t do a ton of damage with her special but she can stop specials from firing, even if it is just for one turn.
Raid defence; she’s annoying as a tank, but not at all intimidating. She’s a meat shield, nothing more. Just there to slow you down enough for someone behind her to do the damage. You know you can take her down easily enough, but she’s probably gonna squeeze that special out and just prolong the inevitable by a turn.
Maps; she can wipe out an entire wave in low-level farming, with high level farming she’s not good enough. She can help get you through late map stages on your first run through, while your team is developing. But if you just want to quickly farm some materials in prov 22 or so, she’s not desirable.