If your wife feels she needs to go to support a close cousin, the rule book says your wife must ask for a Special Exception that can be redeemed at a later date. Your wife must recognize this is a special exception and make the request, not a demand or shaming.
The fact that it conflicts with something that is important to you makes this a Burdened Special Exception. This is next-level. It entitles you to forget your anniversary at least one time or gives you the go-ahead to make comments while watching the Hallmark Channel together for at least a few months.
Like I said, this is big.