Redeka is one of the harder bosses in Act 1, but you can beat her with the right tactic. The core idea of how I approach the fight is to: (1) take out one of the beetles quickly and reset the fight; (2) use Torturer (talent) + Worm Tremor to entangle Redeka and her friends at the backline, and then take out the front 2 zombies and another beetle quickly and reset the fight again; and (3) take out Redeka and friends with Torturer+Worm Tremor combo again.
You'll see you can reset fights quite easily by having a teleporter (i.e. someone with teleportation skill) out of combat and then get them to teleport out a party member who is in combat. If done right both the teleporter and the party member will be out of combat immediately; see 01:22.
My team is all at level 6, and if you're interested in their builds (which aren't particularly optimised), they are:
Geo/Pyro Wizard:
- Core talent: Torturer, Far Out Man
- Core spells: Adrenaline, Worm Tremor, Fireball, Searing Dagger, and other Fire/Earth/Poison spells
Elemental Archer:
- Core talent: Arrow Recovery, Far Out Man
- Core spells: Adrenaline, Elemental Arrowhead, Venom Coating, Enrage
- Core items: Lots of special arrows (poison and water arrows are easy to make)
(Fire) Summoner:
- Core spells: Conjure Incarnate, Farsight Infusion, Power Infusion, Supercharger, Elemental Totem:
- Note: Most of the time I summon the fire version, as Fireball is amazing...
Control Mage:
- Core spells: Adrenaline, Teleportation, Cloak and Dagger, Medusa Head, Spread Your Wings, Blinding Radiance, Electric Discharge, Dazing Bolt
- Note: This is a somewhat odd build, that takes 2x Scoundrel, 2x Polymorph and rest into Aerotheurge. The idea of this character is to run around the battlefield with huge mobility and cast crowd control spells as needed. Also the main teleporter in my team.