I don't have Helianthus. She looks good but I think Tritoma is still better. Or at least, deal way more damages.
Corbett needs good support but she is better than the others. Her damage potential is just insane. As long as Adlay+Zinnia are here, she is free to take her time and do her stuff.
If you must split your teams and want to use Adlay and Zinnia in other teams, she could be replaced. But if you need only one team, there is no reasons to use another girl.
The new Ivy Bride sounds like another good mate for Cattleya. That 5% combo damage for 1 magic attacker is so sweet.
The good team would be Cattleya/Ivy Bride/Angraecum/Vervain (or Chamomille)/Adlay.