From Stage Storm:
Adopted by middle classed parents, Mugiko has always dreamed to be an heiress. Who knew that one day this dream would come true. Mugiko's biological grandfather is the head of a prestigous family and after many years of searching, he finally finds his long lost granddaughter. As she starts her life as an heiress, everyday is filled with excitement, however, everything seems a bit different from what she had imagined, especially when her grandfather plans her engagement with Yoshiki, his previous heir, a cool boy who doesn't aknowledge her as the true heiress.

From JShoujo Scans:

Geraldine Francis is the innocent daughter of a wealthy aristocrat. Being sheltered all her life, she is oblivious to her cousin Charles' true intentions when he lures her in and makes her fall hopelessly in love with him. It is only after the murder of her father that she realizes his love was nothing but love for the money and the land that came with her name. She vows revenge, and she throws away her past in order to become "Silver," the perfect woman. With a new face, and a new lease on life, she will turn the tables on the man whom she once loved so that this time, it is he who will be left with nothing.

Adaptation of English fiction Silver by Penny Jordan.