What Alice does in Eclipse. Keeping up a common theme here...
Being liked by Charlie, she, unlike Edward, has unlimited visitation rights during Bella's punishment for leaving for Italy in New Moon. Alice has a vision of Victoria coming back. After Bella's successful attempt to sneak past Alice's vision to visit Jacob, Edward bribes Alice with a canary yellow Porsche 911 Turbo to kidnap Bella so she won't go to La Push to visit Jacob while he goes hunting for the weekend. Eventually Bella escapes with Jacob while they are at school, but Alice gets her Porsche anyway.
Victoria creates an army of newborn vampires and manages to evade Alice's vision by letting Riley choose her warriors, but Bella figures out her plan and tells Alice this on graduation day. They decide not to tell Edward, so Alice must keep her mind busy all day. That night at the graduation party, she receives a vision of the army's coming and the family prepares a battle strategy led by Jasper, while also forming allegiance with the wolves. During the fight training, Alice uses her visions to become the only one to be able to defeat Jasper, even including Edward, causing the wolves to become skeptical of her. She fights the newborn army, but Jasper doesn't let her do anything out of fear for her safety and ends up getting mildly injured whilst ensuring she has nothing to do.
Alice is highly upset when she sees a vision of Bella and Edward getting married in Las Vegas and confronts Bella about this. She tries to persuade her to let her arrange an official wedding for them. After the newborn army's threat's over, Bella finally gives in to her wishes, and Alice is visibly thrilled to be her maid of honour and getting to arrange everything for the wedding. Bella also tells her August 13th is the latest date for the wedding, which is one month before Bella's 19th birthday. Alice runs off to tell Esme.