SOLVED. Heroine pretends to be her twin sister and have a baby with twins husband (artificial insemination a course) because sister died in car accidents with her lover.

[Shelia]

Heroine is pretending to be her twin because she asked her to carry her child for her and the hero. She agrees to do this but the twin later dies in a car accident with her lover. So now when the hero comes to the U.S. to get his wife she has to pretend to be his wife. The hero begins to see that his wife is different than the last time he saw here. An when he takes her home to his family and also sees how different she is around his family (his family never liked his wife because of the way she was towards them) because she was very sweet and respectful to his family when the real wife wasn't.

I also remember that the sisters names was were close to the same but the opposite. The twin who died was named Isabelle ??? And the heroine was named ??? Isabelle. (The ??? are the same name i just can't remember what it is) so it was easy for the heroine to pretend to be her sister because they have the same name.