It's good to give advance notice.
Janelle is invited to a wedding for her niece.
Janelle wants to go on a float trip with her friends the same day.
Janelle promptly tells her niece that she can't make it to the wedding, sends a nice gift, and goes on the float trip.
Janelle goes on the float trip and sends her niece a text message saying that she won't be able to make the wedding that day.
Janelle's niece is thankful for the gift.
Janelle's niece is offended that she hadn't told her earlier.