Every date in the planner (her day, the Mass, rehearsals, fittings, payments, tasks) is on the Calendar page, a month at a time.
To see them in your phone's calendar, tap Add to iPhone calendar. On Android or Google Calendar, tap Copy link for Google Calendar and add it in Google Calendar under Other calendars → From URL.
It stays up to date by itself. If you shared the link by mistake, make a new one in Settings; the old one stops working.