From the evite:
Turns out Andrew's family is huge, so to spare you the awkwardness of sitting at a table with a bunch of his relatives, we're having a separate party. JUST FOR YOU! .... Bring your favorite snacks and/or drinks!
She received a STD, so would you take this as... they invited too many people to the reception, sooo now they're hosting a separate party? That's exactly how I took it.