No, it's not appropriate at all. Such topics are private and should be kept within the confines of a respectful relationship. Spreading such stories shows a lack of respect for one's partner and basic decency.
If you hear such inappropriate stories, you should firmly and immediately distance yourself from the person sharing it. Let them know that such topics are unacceptable.
This kind of interest is not in line with the norms of a healthy relationship. A good marriage relationship should be built on positive emotions, common goals and positive communication. You can try to introduce some positive literary works or movies to your wife to guide her interests to a more positive direction.
I'm not sure specifically what this 'sister leaks cum wedding day story' is as it's not a common or well - known general topic. It could be some very specific, perhaps made - up or niche story within a particular group or community.
I'm not entirely sure what this phrase specifically means as 'cum junkie' is a rather vulgar and inappropriate term. However, if we break it down, it seems to be some sort of statement about a person's wife having an excessive or abnormal attraction, which is not a proper or respectful way to describe someone.