We see this a bit differently.
From time to time, we notice people from one of our walks of life--work, hobby, past (university, high school) -- on one of the adult sites. Unless we have some strong reason for contacting them, we will typically pass them by. That said, if you attend an LS event -- even a vanilla meet and greet, to say nothing of a house party or hotel takeover or cruise -- we can more or less guarantee that you will eventually encounter someone you know. "Deer in headlights" is not a helpful reaction.
One way to gauge your own responses is to practice, and here is the departure from others' thoughts: make contact and plan a vanilla dinner to catch up. Up to you whether you want to use SLS as the vehicle (you mentioned that she's on facebook). Find a time together--this might be a "why did you reach out now?" response, or might be a quiet conversation in the ladies' room--to communicate that you know and you will of course protect their confidence.
To repeat, the situation of running into someone you know is more probable than not--you just do not know when. Gaining skill in how to place that information in context of your pre-existing relationship with that person or couple will prepare you for the unexpected.