There are lots of state laws on the books that are invalid and unenforceable. Federal law trumps state law.
So why is Pot legal in Colorado?
I don't believe there is a Fed law on homo marriage, only that they recognize it for purposes of benefits.
SCOTUS only struck down state laws that do not recognize homo marriage thereby nullifying them and leaving them without any authority to recognize any marriage at all. So in this case Davis is completely correct in what she is doing.
To be clear, I don't believe the Fed has any Constitutional authority what so ever in this and in my opinion it is strictly a State issue, KY should tell the Feds to go pound sand.