While I think this is a very interesting situation and I admit I am curious to know what the NPHC orgs position on "dual membership" is, I think it should be left to just that. . .a curiosity. Unless she is doing more than switching to a different org (such as horrible behaviors, bad rep, etc) I don't see how she is making a joke of Greek Life. Her actions will only affect you if you let them. So I wouldn't waste too much energy on figuring out her motives, etc. Just let her be and move on.
When I joined a sorority, I personally joined for life. Same thing for my university. I am a Reddie and always will be. Same thing for my marriage. My first and only one (barring extreme circumstances such as death or abuse). That is how I approach my committments in life. . .as committments FOR life. Not everyone values committments in the same way. And that's OK. If I figure that out about someone, then I use that information in determining how much I trust them. But I don't necessarily fret over it.
My suggestion is that you don't fret over it either.
