I agree, if she knows that the AFA is her #1 choice, she should decline the WP spot ASAP. Remember there will be a cadet at WP whose life is basically in her hands, would you want her apptmt to the AFA held up because of a candidate at WP if roles were reversed?
Whatever that could happen to her in the future to preclude her from attending the AFA will most likely be true for WP. There is a difference from hedging bets (1 apptmt and waiting for the second) and holding an apptmt for Just In Case.