Nice misunderstanding of facts here.

The church wedding for members of our church happens in a place we call temple. Temples are not our churches, they are a sacred place that only members in good standing are allowed to visit. This is not the place we meet at every week for our weekly church services.

So yeah, that parent would not be allowed to go to the temple, where the wedding ceremony happened. But that parent would not be excluded at all for the rest of the wedding and/or any other kind of communication with their child.

In the eyes of the church, someone who has been excommunicated has the exact same status as someone, who has never been part of the church.

It's quite interesting to me, how many people believe they know more about the church than members of said church, because they know someone who knows someone who said a thing.

But I guess it's not surprising, since also lots of people who never actually met a trans person strongly believe they really understand trans people and their supposed evil motivations.