Children are not disposable. They are a commitment for life (or at least till 18) and are the product of what personal they experience growing up.
This poor kid has been discarded by her mother. Now her father's new family is taking over her life.
If she does not like the decoration let her change it.
To ask the artist to destroy her own gifted work yet shows a total lack of respect for his sister and her efforts. If this is how he treats people in general his dd will likley be a delinquent teen.
Sorry for rant. Off soap box now