Just after William had witnessed Samantha kill Nicola, William came to her house and told the family before blackmailing them, Veronica witnessed all of it as she sat by quietly. ("I Spy With My Little Eye")
While walking down a street one day, Veronica started to feel a bit sick and dizzy. Her parents said they would take her to the doctors soon. After Rose had asked the family if they'd seen her dog, Veronica suddenly fainted.
Later on, at the hospital, after being tested, Christian diagnosed her with Cancer. She then died an unknown amount of time later, and her family and friends attended her funeral. ("Pax Postremo")