Awakened Jessica will generally outperform silver heavy armors. Jessica has less physical mitigation than Leeanne or Bernard during Increase Defense but she also has enough of a hp advantage to avoid being one shot killed by anything that would fail to kill a silver heavy armor. Using her puts a bit more stress on your healers than with other tanks but in exchange you get some nice MR and solid aoe damage. She'll remain a solid anti-swarm unit and backup tank even if you do happen to score a Bernice, Gellius or Deine later on, so I'd go ahead and invest in her with little regret.