According to ProFootballTalk, it is possible that the unnamed therapist that Brett Favre texted may join the lawsuit as a plaintiff. Favre only texted the unnamed therapist and did not text either plaintiff directly (although he mentioned one plaintiff in a text).
Here is a passage from the article:
Lawyer David Jaraslowicz, who represents Christina Scavo and Shannon O’Toole, said during a Wednesday appearance on ProFootballTalk Live that the unnamed massage therapist to whom the alleged advances were directly made could be joining the lawsuit.
“As a matter of fact, I’ve been contacted by her,” Jaraslowicz said, “but I’m not free to give any information at this point.”
“So what you’re saying is it’s possible she’ll be joining the lawsuit at some point in the future?” said the Internet hack who hosts the show.
“Possible,” Jaraslowicz said.
There is a short video clip of the interview. The lawyer for the plaintiffs indicates he was contacted by the unnamed therapist and that it's possible she could join the suit. It's not clear whether "possible" means "likely" at this point, or if this is designed to apply pressure on the defendants to settle.