In the episode that aired on July 20, 2015, Teller drew a correct explanation for Kyle and Misti's ring escape act. Here's my thought how Misti escaped the rings:
The rings were scrutinized by the audience members. Well, most of the rings were examined. One ring was in Kyle's hand on stage at the beginning. That ring was placed in the bottom most position. I believe that specific ring may have been able to be opened by Misti. Then she dropped down and slipped out the bottom.
Or maybe the bottom ring could bend up far enough to allow Misti slip out. Then she pushed it back into place as she exited.
Even if the bottom ring was legitimate, then a flexible short person would be able to contort through the bottom ring.
I also noticed Misti's hair was slightly out of place right after the act. Possibly due to squeezing through a narrow escape opening.