In chapter 7 of Frankenstein, Victor says the following:
Time had altered her since I last beheld her; it had endowed her with loveliness surpassing the beauty of her childish years. There was the same candour, the same vivacity, but it was allied to an expression more full of sensibility and intellect. She welcomed me with the greatest affection.
Although she is distraught over the death of William, Elizabeth is the paragon of the matriarch--concerned over children and family above herself. As such, Shelley characterizes many of the women in the novel as passive victims of sexism. Nearly all of the decisions and activity in the novel is done by men.
The women, like Elizabeth here, seem only to write letters, wait by the bedside, and suffer at the hands of men. Elizabeth, overall, is a suppliet--one whose suffering and victimization by the Monster is a result of Victor's tragic mistakes.
When Frankenstein left to go away to school Elizabeth was a young exuberant girl. They had grown up together and she was a young girl when she was first brought into the home. She is still a younger woman and not yet in the prime of womanhood hen he left to go to school.
Later after Elizabeth had spent years worrying about Victor she has become a woman, but she is drained and the worry can be seen on her. He still finds her beautiful and knows that they are meant to be together but his creation of the creature has blocked the way for them.