According to FZ in The Real Frank Zappa Book, Fishman is a real live person who is proud of her exploits with MOI and post-MOI band members and other members of the vegetable kingdom.
In The Real Frank Zappa Book, Zappa relates a story of his introduction to Fishman in the late 1960's. Fishman won a contest put on by a local promoter and radio station in which contestants were asked to describe how Zappa's music had affected their lives, and Fishman won the contest by saying that since hearing "Call Any Vegetable" she had started using them "internally" and they had benefitted her greatly. We are told that Fishman showed up to meet Zappa with a perfectly spherical ball of her own shit in a mason jar, and presented it to Zappa, who had not known about the contest or the meeting in advance. Bassist Jim Pons, was fascinated with the article and opened it to smell it while waiting for the elevator at the hotel. He made some kind of "wheeeouw!" sound and then dumped the jar with the shit in the trash can outside the elevator.
Stevie's Spanking is a detailed report of an evening Steve Vai spent in a hotel room with Fishman, as reported to Zappa at the following morning's breakfast. Specifically, Zappa refers to Fishman making Vai "drool on his own dork" before "giving it a wanking".
Clearly, Fishman was a true supporter of Zappa's music, to the point of actually providing documentable activities, from the late 1960's through the mid 1980's.
All of the above from The Real Frank Zappa Book