To replace the present forms will and can with the past forms would and could might change the meaning.
The past form had (had to tell) indicates that the choir director's conversation with the event organizer took place at some time before she spoke to the press.
The present forms, with the present form says, indicate that at the time of writing any cancellation or alternative arrangement lay in the future: the event had not yet been cancelled.
The past forms would and could would not exclude this reading; but they would also accommodate a situation in which cancellation or rescheduling did take place, after the conversation took place but before the director spoke to the press and the story was written.