“Celebrate” is an objective term, a verb that is not necessarily representative of a person’s feelings. ".
Nodito a real-world thing/event is rarely totally consumed by a single human word or concept. This is not about Gemma’s feelings, its about whether the word you use to exclusively define this event is realistically appropriate - whether it does complete justice to the situation. I say it does not, and it fall shorts of the reality by many metres (or yards if you are US). Therefore any ethical conclusions based on such an appellation, if not fully applicable, will also fail.
If you look at a cylinder from its side…yes you “objectively” see a rectangle.
If another looks at it from the bottom…they will see a circle.
Both persons are “objectively” correct yet both are limited and incomplete 2D grasps of a bigger reality that is in fact 3D and cannot be fully consumed by such “subjective” 2D angles/interpretations.
That is what I believe you are attempting to do here.
The actual reality at hand is quite ambiguous and nothing like the happy first wedding celebration of two 25 year-old virgins. One might, in dictionary speak, call them both “wedding celebrations” but I suggest the the predication is hardly equivocal for rational thinking persons. Some on this thread would say even the use the common appellation “wedding” is mistaken!
Given this clear ambiguity I believe one cannot validly make the “apriori judgement” (one where we don’t need to investigate any particular examples) that you are suggesting.
It would seem an “aposterior’ judgement” (i.e. a prudential, conscience based judgement based on investigating the actual case in hand and the applicability of the sort of apriori principles you have enunciated) is more reasonablely required in this situation.
That prudential judgement re attending is for Gemma alone to make and, depending on the dictates of her conscience and her better objective understanding of the event than we have, her decision could validly go either way.
Gemma’s mere attending to show filial support her dad in an important event in his life (which may or may not be a formal attempt to confect an invalid natural marriage) is a difficult conundrum readily understood by attending adults. This contradictory reality for immediate family members is readily understood by attending, non-autistic adults these days and so it seems hardly a case of “objectively” and formally approving, as yet unproven, adultery.