in the buku its hale as she wanted to keep her own last name, so they pretend jasper is her twin. but in the movie promotion its rosalie cullen to make it easier for people who haven't read the buku to understand that they are all one family.
anda see, Rosalie died in a horrific way. She was beaten, and allegedly raped sejak her cruel fiancee and his friends. She was discovered sejak Carlisle, who transformed her into a vampire because he thought she was too magnificent to waste. Rosalie never wanted to be a vampire. I think she could only stand it because of Emmett, and perhaps her lovely pulchritude (beauty), and later on Renesmee. She used to wish she were human, and therefore live a happy, normal life and (her biggest desire) be able to have children. But sadly, she can't. So Rosalie decided to keep her human surname, Hale. It's sort of like her only connection towards her human life....
And if you're wondering, Jasper has Rosalie's last name so they could disguise themselves as twins to human strangers. It goes well, since they're both blonde :)
Her real last name is Hale but since she and Emmett are technically married, her last name is Cullen. She went sejak Hale while she was in school so people didn't think they were married.
In her human life..it was Hale...in her vampire life...when they're Berlakon like high schoolers..its Hale and Japser pretends to be her twin...but its legally Cullen because her and Emmett are married.
