Is it permissible for an unmarried woman to pray Istikharah concerning marriage, before anyone proposes to her?

Seeking guidance (Istikhara) to discern if a marriage is good for a girl is permissible, and it should be performed when a man proposes to her, because Istikhara is done when one intends to act or refrain from acting. However, performing Istikhara to know the time of marriage is not permissible, because that is part of the unseen, which no one knows except Allah.