What is not appreciated about the death of a loved one is that “Death ends a life but it doesn’t end a relationship that lives on in the mind of the survivor.” Some studies have shown that mourners hold onto the relationship with the deceased with no notable ill effects.
A childhood death of a parent can be a devastating event.
One way I think this is appropriate is to mention her in the wedding program and/or light a candle during a portion of the ceremony that names those who are “special to us but not here to share this day.” I have seen an acknowledgement of special friends and family who are deceased but remembered on this special day.
A paragraph, properly worded, could mention your mother’s role in raising you, making you who you are today, and how you wish she were here to share this occasion.
How the child grieves is extremely individual and based on the child’s age when the parent died, the cause of the loss, the quality of the parent-child relationship prior to the death, and the support system available both at the time of the loss and afterwards.