Gwendolyn Weapon refinery

Without having used her much myself, probably want to play to her strengths. +Def to keep her tanker or +Atk would be safe bets. Even with a speed boon, it's unlikely she avoids doubles or doubles herself, so just keep building her as a Tank and let her roll.

That really depend on the build I guess.
DC build would want +Res.
Otherwise, atk or def for melee tank