Underworld: Awakening

Six months after the events of Evolution, the government, as well as the general public, have become aware of the existence of vampires and Lycans. An initial program to study and harness their potential powers and scientific applications soon escalates into an all-out genocide. Shortly after the "Purge" begins, Selene and Michael are captured by humans. Due to her enhanced vampiric traits, she is imprisoned in cryogenic suspension.
After being frozen for 12 years, during which time both species have been hunted to the brink of extinction, Selene manages to escape. She soon learns that another subject has also escaped the same facility, whom she initially believes to be Michael. As she makes her way through the high-tech facility, Selene sees flashes of someone else's point-of-view. Believing that Michael is mentally guiding her, she follows these "visions", which lead her down a garbage chute into a labyrinthine series of basement tunnels, where she encounters a young vampire named David, who has been tracking her. They quickly realize that the tunnels are infested with Lycans, who are hunting the subject Selene is connected with. Determined to reach Michael, Selene fights her way through the Lycan onslaught until she reaches the second escapee; not Michael, but a frightened and confused young girl named Eve.
Using David's van, they start to make their way out of the facility, only to be attacked once again by a trio of Lycans. David manages to shoot one while Selene stabs another; but the third smashes its way into the rear of the vehicle, where it bites Eve's shoulder, which triggers Eve's partial transformation, revealing her hybrid traits as she savagely rips the creature's head in half. Selene realizes that Eve is her and Michael's daughter. Eve is believed to be the key to ending the war by "curing" both the vampiric and Lycanthropic "infections". However, despite her hybrid nature, Selene soon realizes that Eve's bite wound is not healing and she is rapidly growing weaker. David agrees to take the pair to his coven.
The vampires realize that Eveâs weakness is due to her not feeding in a long time. After reluctantly drinking some blood, her wound closes up. Seeing that the coven does not want her there, Selene gets ready to leave. David tries to convince her to stay and help them start an offensive against the humans by training some Death Dealers. Before she makes up her mind, the coven comes under attack by Lycans. Selene joins the fight and kills many of the Lycans. She then finds herself facing a "Super-Lycan" that heals instantly and is not affected by silver. She is knocked out and awakens later to find that Thomas, David's father, surrendered Eve to the Lycans to placate them into leaving. David dies but is resuscitated. Selene confronts a human detective named Sebastian, who is sympathetic to the vampires after learning his wife was one. Sebastian confirms that the Lycans have been traced to Antigen, the corporation dedicated to killing off the immortal species and runs the facility Selene escaped from in the beginning.
Selene discovers that Antigen is actually run by Lycans, who have been posing as humans in order to trick the world's governments into believing the Lycans are extinct. The director of Antigen, Dr. Jacob Lane, is trying to perfect the Lycan race and wants Eve's DNA. The "Super-Lycan" Selene faced earlier is actually Quint - Lane's son and the prototype for the new modifications. Selene and Sebastian infiltrate Antigen to stop Lane's plans and save Eve. Selene comes across Subject 0, realizes it is Michael and attempts to free him by shooting his cryogenic tank. She is forced to leave the thawing Michael in order to stop the Lycans from leaving with Eve. After confronting Lane and his son, Selene and Eve return to Michael's tank and find it empty with the ice shattered. Selene states that the world will be hunting Michael, and the pair promise to find him first.

Question: What causes Eve's weakness?
Answer: Not feeding in a long time