Thise vibration dampeners were donnay I think - basically just a piece of foam.
The Donnay Vibrazorb! Hated those; looked goofy.
It must be Prince's version, as you can see the "P" logo, if you zoom the second picture.
Her last GS with POG was Wimbledon 1990, where she lost in the QF. In her first Grand Slam with a Yonex racket (US Open 1990), her tournament ended in the third round. Still using this type of dampener. She won the Australian Open in 1991, with Yonex dampener between the strings.