Modern AU, Anna is 15 and Elsa is 21
Elsa and Anna Arendelle weren't what you called "close", especially since Elsa had shut Anna out since childhood, but this all changes when they're all they had left.
When their parents die, Elsa gains legal guardianship over Anna, and she's forced to let her in, and the two sisters have a lot of making up to do. But as life gets in the way, with Anna in her sophomore year of college, dealing with typical high school issues of bullying, drama and boys, and Elsa as an overworked college student, trying to earn a degree in architecture, while working to provide for her and her sister, and her past haunting her.
Through these troubles, the sisters will gain a closer bond and help each other through these issues.
Once Elsa's ice powers are finally accepted by the people of Arendelle, Anna and Elsa are finally able to live a 'normal' lifestyle. The gates remained opened, more parties were held, and the two sisters were talking again. They had finally caught up with each other. They had become as close as they had been when they were children.
Anna and Kristoff's relationship was off to a good start too. She had just presented him with a brand new sled followed by an awkward first kiss. This kiss was followed by more as their relationship grew stronger and stronger. But when Kristoff proposes to Anna's for her hand in marriage, something goes terribly wrong...
(A Kristanna Fanfiction - starts the day after the movie ends)