Complex sentence: She however was so shocked and dismayed at the loss of her principal minister, that she gave Apokaukos'supporters, who were joined by the "Gasmouloi", the fleet's marines, free rein to avenge their leader's death.
Split into simpler sentences: She however was shocked and dismayed at the loss of her principal minister. Thus Apokaukos'supporters, who were joined by the "Gasmouloi", the fleet's marines, were allowed to avenge their leader's death.