I think you're having trouble because most publications refer to "trans disposability" rather than exclude the concept to transfems. This paper defines it:

Building on Henry Giroux’s concept of a biopolitics of disposability, I show how these memes present trans people as disposable: excluded from public view and liable for prosecution for existing in public space...

The biopolitics of disposability works by making marginalized people disappear from public view by regulating their bodies into invisibility. They are, in a word, disposable.

That's an interesting phrase. From a cursory search it looks like it's a labeling for the way trans people are being legislated out of existence/the public eye.