Weddings are an expensive business, your daughter does not want to pay for people who then walk out and waste the food provided. If she is planning a sit down meal the costs of a large number of people leaving the venue could be significant and disruptive. Sorry to talk money in a moral dilema but it is a consideration.
If she wants to invite the Df'd relative she should be free to do so but I would notify the JW relatives she intends to invite that he will be attending, thus giving them the opportunity to decline if their conscience is offended . She can then have people attending her wedding who are thinking about her happiness and not their religious rules. Often at weddings we invite people out of duty when in fact we should invite people who love and care about us and want to share in our happiness.
It is her day and so she should not have to deal with any dramas on the day, JW relatives causing a scene is an embarrassment and could spoil the day for everyone. The other solution is to take the decision out of their hands and not invite them at all or invite them to the ceremony but not the reception.
Have you talked to your daughter about this? What would she prefer and how does she feel about her JW relatives, does she want them there or are they being invited because they are relatives. You may be worrying about something that she has already thought about.
