Well, Irina is definitely not 26. She's more like 1,000 and counting. This 'Twilight' character, portrayed by actress Maggie Grace (shown above), did attend the Swan-Cullen wedding, but she doesn't stay all that supportive of the family.

SPOILER ALERT -- Irina's Denali, Alaska-based family had a run in with a turned vampire child centuries ago. Unable to control its strength or thirst, the child, which unlike Renesmee became a vampire through bite not birth, wreaked havoc on the human population. The Volturi had to step in and destroy all those involved, but Irina and her sisters were spared. It's this memory that prompts her to ultimately betray the Cullens to the Volturi.