Jessica shared a couple of snapshots of the celebration on Instagram Monday night, where she showcased attendees posing by the pool and showed off her toned body in a black one-piece swimsuit.
"All the beauties celebrating @ashleesimpsonofficial / @missbananahammock!!! I love you Ash :)" the fashion designer captioned the first photo.
"Oh yea girl...We are proud to be in our bathing suits!! @baylormcg #hardworkpaysoff #workoutpartnersforlife," Jessica wrote along another photo.
Ashlee got engaged to Diana Ross' son Evan Ross in January. The pair, together since July of 2013, threw an engagement party in March. There is no word on when they're planning to wed. The marriage would be Ashlee's second as she previously tied the knot to Fall Out Boy rocker Pete Wentz in 2008. They have a son, Bronx Mowgli Wentz, born in November 2008.