What significant event took place on September 16, 2016, for this chapter?

The significant event that took place on September 16, 2016, for the chapter is the First Bid Day. Bid Day is a pivotal moment in the recruitment process for sororities, as it marks the day when potential new members receive invitations or "bids" to join the organization. This event not only signifies the culmination of the recruitment efforts but also welcomes new members into the chapter, fostering a sense of belonging and community from the very start of their Greek experience.

As Bid Day is essential for establishing new relationships and building the chapter’s membership, it holds a special and lasting impact on the chapter's dynamics and activities moving forward. The other options, while important in their own right, do not hold the same level of significance tied directly to the recruitment and membership process of a sorority as Bid Day does. The First Philanthropy Event, First Founders Day Celebration, or First Annual Retreat would also be meaningful events, but they do not encapsulate the immediate excitement and foundational change associated with gaining new members through Bid Day.