Defamation isn't only about truth. It's also about damage.
Surely it would be a compliment to a MAGA female to be Trump's lover, even if it is untrue.
Of course, I have no idea if she is.
There is a second point: her own vile posts do more damage to her reputation than anyone else possibly could. Does she have a reputation to defend? How would "sleeps with Trump" be worse than "makes hate-filled statements about immigrants" and "scurrilous comments Taylor Swift's relationship with Travis Kelsey."