If you can do the full event path, buy a reset. 8 for 300c is better than the 5 chocolate box unless you only need the 5. Roza is okay. Not a massive upgrade over Svetlana, if you have her. Just more damage. A Jack of all trades master of none sort of TD. Her active isn't much, since it provides no special bonus or effect, but she's still quite good for her passive pen and aoe if you don't have Wotan.

Ciara's good dps fielded cheaply but her passive can be a problem. Kristina+ or Seren do passive pen better in the same general role.