Ghoulia will restore her health by devouring your fallen troops. Fashion, feasting, fighting. Everyone's got priorities.
Try to use a high cost Tank like Abomination or Stonehoof Tauren combined with ranged DPS or Unbound Minis to kill Ghoulia in one push!
For every PvE mission, there is a campaign version and a Heroic version. When you first begin the game, you can only participate in campaign missions. Upon collecting 50 sigils, you will then unlock Heroic missions.
Campaign missions will grant rewards after the first successful clear with ANY family. Heroic missions must be completed with EACH of the 5 different families in order to receive the mission rewards.