Why does Valerie seek to ruin Elizabeth's reputation in the novel, Almost Heaven?

Valerie Jamison is the daughter of the woman whom Robert has arranged to sponsor Elizabeth for her debut. Valerie is jealous of Elizabeth and feels that if Elizabeth were ruined her suitors would be available for the rest of the debutantes. Valerie schemes to cause Elizabeth to get caught in a lover's embrace with Ian so that her reputation will be ruined and she will not be able to make a good marriage. Valerie's scheme works at first. However, Ian and Elizabeth eventually realize what has taken place and manage to repair their reputations and their relationship.